SEARCH

SEARCH BY CITATION

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Primary prevention
  5. Clinical trials of prophylactic HPV vaccines
  6. Secondary prevention of cervical cancer
  7. What are the barriers to cervical cancer screening in developing countries?
  8. Visual inspection screening methods
  9. Direct visual inspection
  10. HPV DNA testing
  11. HPV DNA testing methods
  12. HPV DNA testing as a primary screening test
  13. Two-stage screening
  14. Self-testing for high risk types of HPV DNA
  15. Conclusions
  16. References

Cervical cancer remains the commonest cancer cause of death among women in developing countries, largely due to the failure to establish cytologically based cervical cancer screening programmes. There are many barriers to the establishment of screening programmes in poor countries ranging from limited financial, human and health resources to the complex infrastructural requirements of traditional screening programmes. Alternative approaches to cervical cancer prevention are currently being investigated, including primary prevention with prophylactic vaccines against human papillomavirus to alternative screening tests and protocols. These will be explored in this review.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Primary prevention
  5. Clinical trials of prophylactic HPV vaccines
  6. Secondary prevention of cervical cancer
  7. What are the barriers to cervical cancer screening in developing countries?
  8. Visual inspection screening methods
  9. Direct visual inspection
  10. HPV DNA testing
  11. HPV DNA testing methods
  12. HPV DNA testing as a primary screening test
  13. Two-stage screening
  14. Self-testing for high risk types of HPV DNA
  15. Conclusions
  16. References

The huge disparities in wealth between developed and undeveloped countries are well illustrated in the types of cancers prevalent in the different communities. For instance, due to extensive screening of women in many developed countries, whether performed in the context of organised programmes (as is the case in the United Kingdom) or unorganised programmes (as in the United States), cervical cancer has become a relatively rare disease.1 However, in countries that lack screening programmes, cervical cancer remains the most common cancer cause of death. Thus, it would be accurate to state that cervical cancer is a disease of poor women, representing inequity of access to health care resources, such as cervical cancer screening.

Globally, cervical cancer comprises approximately 12% of all cancers in women and it is the second most common cancer in women worldwide, although the most common among women in developing countries. In the year 2000, the global estimate was of 470,600 new cases and 233,400 deaths from cervical cancer each year.1 Eighty-three percent of these cases were found in developing countries that have access to only 5% of global cancer resources.1 The highest incidence rates of cervical cancer are in Latin America, sub-Saharan Africa and South and Southeast Asia where cervical cancer accounts for approximately 15% of all cancers. By contrast in developed countries, cervical cancer comprises about 4% of all cancers and is the sixth most common cancer in women.2

There is now a considerable body of epidemiological, clinical and molecular evidence that persistent infection of the cervix with high risk types of human papillomavirus (HPV) is necessary for the development of cervical cancer. High risk types of HPV are identified in nearly all carcinomas of the cervix and the relative risk of cervical cancer associated with infection with high risk types of HPV is higher than the risk of lung cancer associated with smoking.3 Munoz et al.4 pooled data from 11 case–control studies involving 1918 women with histologically confirmed squamous cell carcinoma of the cervix and 1928 control women. The pooled odds ratio for cervical cancer associated with the presence of any HPV was 158.2 (95% CI: 113.4–220.6). On the basis of the pooled data, 15 HPV types were classified as high risk types (16, 18, 31, 33, 39, 45, 51, 52, 56, 58, 59, 68, 73 and 82) and are considered carcinogenic.

In a meta-analysis of HPV types found in invasive cervical cancers worldwide,5 data on a total of 10,058 cases (which included squamous cell carcinomas, adenocarcinomas and adenosquamous carcinomas) confirmed the high prevalence of HPV in cervical cancers in different regions of the world with HPV 16 (51%) and 18 (16.2%) being the most common. However, more than 16 other types of HPV were also associated with cervical cancer, of which types 45, 31, 33, 58 and 52 were the most prevalent. Further, HPV 16 types were more prevalent in squamous carcinomas and HPV 18 types more prevalent in adenocarcinomas of the cervix. Overall, HPV prevalence differed little between geographical regions (83–89%) but was low compared with the almost 100% prevalence in studies that have used the most sensitive methods of detection for HPV.3

There is good evidence that HPV infection precedes the development of cervical cancer by a number of decades and that persistent infection with HPV is necessary for the development of and progression of pre-cancerous lesions of the cervix, either to higher grades of pre-cancerous disease or to cancer3 [pre-cancerous lesions of the cervix in this article will be referred to either as cervical intraepithelial neoplasia (CIN) or squamous intraepithelial lesions (SIL)].

Cervical cancer offers two unique opportunities for prevention of cancer, at both primary and secondary levels of intervention in the natural history of the disease. Primary prevention requires prevention of HPV infection, and there are currently two published clinical trials on the efficacy of prophylactic HPV vaccines in preventing HPV infection that will be presented in the next section. Secondary prevention detects and treats cervical cancer precursors, traditionally using cytology as the primary screening test, although there have been a number of recent trials of alternative methods for the detection of cervical cancer precursors, specifically visual inspection methods and HPV DNA testing. Once cervical cancer precursors are detected, treated and followed up to detect recurrence, progression to cancer can be halted and cancer prevented. This article will review both primary and secondary prevention of cervical cancer, particularly from the perspective of developing countries.

Primary prevention

  1. Top of page
  2. Abstract
  3. Introduction
  4. Primary prevention
  5. Clinical trials of prophylactic HPV vaccines
  6. Secondary prevention of cervical cancer
  7. What are the barriers to cervical cancer screening in developing countries?
  8. Visual inspection screening methods
  9. Direct visual inspection
  10. HPV DNA testing
  11. HPV DNA testing methods
  12. HPV DNA testing as a primary screening test
  13. Two-stage screening
  14. Self-testing for high risk types of HPV DNA
  15. Conclusions
  16. References

The very strong association between HPV infection of the cervix and cervical cancer is now regarded as causal.3 This has profound implications for prevention of cervical cancer because, if the above assertion is true, then prevention of infection by HPV should eliminate cervical cancer. HPV infection is transmitted mostly via the sexual route, with other forms of transmission such as autoinoculation, maternal to child or horizontally playing a marginal role in acquisition of infection of the genital tract.

Papillomaviruses are double-stranded DNA viruses that infect squamous or mucosal epithelia. The HPV virus consists of a non-enveloped capsid containing the major structural protein L1 and a minor capsid protein L2. Within the virus is the double-stranded DNA genome bound to cellular histones. Exactly how the HPV capsid proteins interact with cellular receptors is not well understood; however, antibodies to L1 and L2 can block HPV infection.6 In the episomal state in the host cell, the HPV genome expresses proteins coded for by the E1 and E2 regions as well as E6 and E7.7 In productive infections, HPV remains in the episomal state, but in cancers, the HPV genome becomes integrated into the host genome. Integration into the host genome leads to changes in the gene expression that result in the upregulation of E6 and E7 genes and their proteins. These oncoproteins appear to be necessary to the oncogenic transformation of infected cells.

The target of choice for prophylactic vaccines is the viral particle composed of the capsid proteins L1 and L2. Animal and human studies of papillomavirus infection have provided good evidence that neutralising antibodies to these proteins can block new infections with HPV.8,9 For prophylactic vaccines, empty viral capsids called virus-like particles (VLPs) are synthesised from microbial or cellular expression systems. Early studies of HPV 16 L1 VLP vaccines showed that they were well tolerated and generated high levels of antibodies against HPV 16.10

Clinical trials of prophylactic HPV vaccines

  1. Top of page
  2. Abstract
  3. Introduction
  4. Primary prevention
  5. Clinical trials of prophylactic HPV vaccines
  6. Secondary prevention of cervical cancer
  7. What are the barriers to cervical cancer screening in developing countries?
  8. Visual inspection screening methods
  9. Direct visual inspection
  10. HPV DNA testing
  11. HPV DNA testing methods
  12. HPV DNA testing as a primary screening test
  13. Two-stage screening
  14. Self-testing for high risk types of HPV DNA
  15. Conclusions
  16. References

The first randomised clinical trial of prophylactic vaccines published was a double-blind, multicentre, randomised clinical trial designed to determine whether an HPV 16 L1 virus-like particle vaccine could prevent HPV 16 infection in women.11 Koutsky et al. recruited 2392 non-pregnant women aged 16–23 years who reported no more than five male sex partners during their lifetime. Women were randomly assigned to receive the HPV vaccine or placebo on day 0, month 2 and month 6. Overall, 1533 women were included in the primary analysis and were followed for a median of 17.4 months after completion of the vaccine regimen. The most common reason for exclusion from the study was evidence of HPV 16 infection at enrolment. The incidence of HPV 16 infection was 3.8 woman-years at risk in the placebo group and 0 per 100 woman-years at risk in the vaccine group (i.e. 100% efficacy). All 41 cases of HPV 16 infection occurred in the placebo group (including nine cases of HPV-16-related CIN). Further, of women receiving the vaccine, 99.7% seroconverted and the antibody titre to HPV 16 was 58.7 times as high as the titre among women with serologic evidence of natural HPV 16 infection at enrolment. The duration of the antibody response and protection remains to be determined.

In 2004, Harper et al.12 reported on a randomised controlled trial of a bivalent L1 virus-like particle HPV vaccine against subtypes HPV 16 and 18 in which 1113 women from North America and Brazil, aged 15–25 years, were randomised to received three doses of vaccine at day 0, 1 and 6 months or placebo, with a 27-month follow up post-vaccination. Their study showed that the vaccine had a 91.6% efficacy against incident infection and 100% efficacy against persistent infection. In addition, the vaccine was found to be safe and well tolerated by the participants.

These two studies provide convincing evidence that prophylactic vaccines are effective at preventing new and persistent HPV infections of the genital tract with the two most common types of HPV associated with cervical cancer and its precursors. However, there are many unanswered questions regarding HPV vaccination and its ability to prevent cervical cancer, particularly in view of the types of HPV other than HPV 16 and 18 that are strongly associated with cervical cancer. In addition, duration of protection from vaccination is not yet known and long term follow up of vaccinated women is required before the impact on cervical cancer prevention can be fully determined. The published results of these two randomised controlled trials are encouraging and may have major implications for developing countries where the establishment of secondary prevention of cervical cancer programmes have to date mostly failed.

Secondary prevention of cervical cancer

  1. Top of page
  2. Abstract
  3. Introduction
  4. Primary prevention
  5. Clinical trials of prophylactic HPV vaccines
  6. Secondary prevention of cervical cancer
  7. What are the barriers to cervical cancer screening in developing countries?
  8. Visual inspection screening methods
  9. Direct visual inspection
  10. HPV DNA testing
  11. HPV DNA testing methods
  12. HPV DNA testing as a primary screening test
  13. Two-stage screening
  14. Self-testing for high risk types of HPV DNA
  15. Conclusions
  16. References

There have been no randomised controlled trials to evaluate the impact of cervical cancer screening on cervical cancer incidence and mortality and all data on the effect of screening has come from cohort and case–control led studies. However, the marked reduction in the incidence of and mortality from cervical cancer before and after the introduction of screening programmes in a variety of developed countries has been interpreted as strong non-experimental support for organised cervical cancer screening programmes.

The International Agency for Research on Cancer (IARC) conducted a comprehensive analysis of data from several of the largest screening programmes in the world in 1986 and showed that well-organised screening programmes were effective in reducing the incidence of and mortality from cervical cancer.13 In addition, they showed that the extent to which screening programmes have succeeded or failed to decrease the incidence of and mortality from cervical cancer is largely reflected in (1) the extent of coverage of the population at risk by screening, (2) the target age of women screened and (3) the reliability of cytology services.14,15

What are the barriers to cervical cancer screening in developing countries?

  1. Top of page
  2. Abstract
  3. Introduction
  4. Primary prevention
  5. Clinical trials of prophylactic HPV vaccines
  6. Secondary prevention of cervical cancer
  7. What are the barriers to cervical cancer screening in developing countries?
  8. Visual inspection screening methods
  9. Direct visual inspection
  10. HPV DNA testing
  11. HPV DNA testing methods
  12. HPV DNA testing as a primary screening test
  13. Two-stage screening
  14. Self-testing for high risk types of HPV DNA
  15. Conclusions
  16. References

The health profile among women in developing countries is dominated by the high prevalence of communicable and infectious diseases and maternal morbidity and mortality. There are many barriers to establishing cervical cancer screening programmes in low resource settings. These include the demands of competing health needs, particularly infectious diseases such as tuberculosis and malaria to name a few, maternal and infant mortality and more recently the HIV pandemic. Health care services tend to be poorly developed and those that exist tend to be focussed on curative, rather than preventative health care. War and civil strife are endemic in many poor countries with devastating consequences for health care infrastructure. Women in poor countries are often uninformed about interventions such as cervical cancer screening; thus, there is no consumer demand and no real political will to establish screening programmes. There is also widespread poverty in many developing countries and in sub-Saharan Africa only 25% of the population have access to safe water and sanitation.16 The average yearly per capita expenditure on health in most African countries is approximately US$3 compared with US$ 5000 in the USA (4) (http://cms.hhs.gov).

In addition to the formidable barriers created by socio-economic conditions in poor countries, the traditional method of screening, cervical cytology, presents a further barrier. Cytologically based screening programmes require a relatively sophisticated infrastructure, including highly trained personnel, built in quality control, ongoing training of staff, adequately equipped laboratories and functional referral systems to communicate results of the test (which is usually delayed) to women. Moreover, cytological screening is coupled with colposcopic evaluation and histological sampling before treatment. Colposcopy requires a level of clinical expertise typically found only in tertiary or urban health care facilities, if available at all and histology requires a laboratory infrastructure and trained pathologists, all of which are in short supply in poor countries.

Finally, there is increasing recognition of the limitations inherent in cytology screening. Recent meta-analyses have suggested that a single conventional cervical smear misses between 40% and 50% of biopsy confirmed high grade SIL and cervical cancers.17,18

Because of the problems intrinsic to cytologically based screening protocols, considerable attention is being paid to developing alternative screening methods, such as visual inspection methods and HPV testing, as well as alternative management protocols for the prevention of cervical cancer in low resource settings. Ideally, for low resource settings, screening should be performed at a primary health care level, using trained nurses or paramedical staff, whether in an urban or rural setting. The screening test should be a low technology test and one that provides either an immediate result (as is possible with simple visual screening methods such as direct visual inspection or DVI) or a rapid turn around of results (as is possible with HPV DNA testing), particularly in settings where transport and communication technologies (even postal services) are lacking. Linking screening to treatment and eliminating the intermediate steps of colposcopy and histological sampling may not only reduce the costs and infra-structural requirements of screening, but may increase women's compliance with screening protocols.

Visual inspection screening methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Primary prevention
  5. Clinical trials of prophylactic HPV vaccines
  6. Secondary prevention of cervical cancer
  7. What are the barriers to cervical cancer screening in developing countries?
  8. Visual inspection screening methods
  9. Direct visual inspection
  10. HPV DNA testing
  11. HPV DNA testing methods
  12. HPV DNA testing as a primary screening test
  13. Two-stage screening
  14. Self-testing for high risk types of HPV DNA
  15. Conclusions
  16. References

Historically, visual inspection of the cervix was the first method of screening of the cervix, introduced in the 1930s by Schiller,19 who used Lugol's iodine to ‘increase the number of clinically diagnosed leucoplakias by making visible the lesions which would otherwise escape the naked eye’. It was however soon realised that this method of screening had very poor specificity and Schiller's test (as it was known) was rapidly replaced with cytology when it became available.

The resurgence of studies evaluating visual inspection of the cervix as a screening tool are as numerous as they are heterogenous, with many different techniques described, use of different terminologies to define positive tests and different study designs.

Direct visual inspection

  1. Top of page
  2. Abstract
  3. Introduction
  4. Primary prevention
  5. Clinical trials of prophylactic HPV vaccines
  6. Secondary prevention of cervical cancer
  7. What are the barriers to cervical cancer screening in developing countries?
  8. Visual inspection screening methods
  9. Direct visual inspection
  10. HPV DNA testing
  11. HPV DNA testing methods
  12. HPV DNA testing as a primary screening test
  13. Two-stage screening
  14. Self-testing for high risk types of HPV DNA
  15. Conclusions
  16. References

DVI [also known as visual inspection with acetic acid (VIA), cervicoscopy, the acetic acid test or the vinegar test] requires that a woman lie in the lithotomy or supine position, a speculum is passed to visualise the cervix and the cervix is then washed with a dilute solution (3–5%) of acetic acid for approximately 1–2 minutes. Thereafter, the cervix is examined with the naked eye or with a hand-held magnifying device (usually 4× magnification) and an adequate light source. The acetic acid causes ‘whitening’ (known as ‘acetowhitening’) of epithelial cells that contain a high nuclear–cytoplasmic ratio. A range of epithelial changes will appear acetowhite after the application of acetic acid and these include immature squamous metaplasia, infection of the cervix with HPV (both low and high risk types) and true cervical cancer precursors. Unlike colposcopy, which examines the cervix in greater detail (types of vessels found within acetowhite lesions, the quality of the margins, surface configuration, contour and colour of the acetowhite lesions) and which uses significantly higher magnification, DVI in most studies determines the presence or absence of an acetowhite lesion in the region of the transformation zone of the cervix.

DVI has been evaluated in a number of large clinical trials, some evaluating DVI alone and others compared with the performance of cytology and HPV DNA testing. Definitions of a positive DVI test have varied, as have training techniques. Most studies have been cross section al in nature, and have been limited by verification bias, in that the ‘gold standard’ (usually colposcopy and/or biopsy) has only been applied to those with positive tests, making the diagnosis of disease in women negative for screening tests impossible. Verification bias tends to over-estimate the specificity of the test. Most studies have used high grade cervical cancer precursors and/or cancer as the outcome measure. High grade cervical cancer precursors are also known as CIN grades 2 and 3 or high grade squamous intraepithelial lesions (HSIL), which encompasses the diagnoses of CIN 2 or 3.

Table 120–29 lists some of the larger cross-sectional studies published, where colposcopy and/or biopsy were used to establish the presence of high grade cervical cancer precursors or cancer. A relatively wide range of estimated sensitivities and specificities are reported, although all show sensitivities of greater than 60% with most reporting relatively low specificities and positive predictive values (PPVs). All, however, reported high negative predictive values (NPVs), which has important implications for national screening programmes. Details of some of these studies are given below.

Table 1.  Results of studies using direct visual inspection as a screening test.
AuthorCountryNumber of casesDetection of HSIL and Cancer
Sensitivity (%)*Specificity (%)*
  • *

    Estimated from numbers provided in manuscript and may not reflect adjustment for verification bias.

Ottaviano and La Torre (1982)20Italy240094*90*
Cecchini et al. (1993)21Italy21057575
Megevand et al. (1996)22South Africa24266698
Sankaranarayanan et al. (1998)24India21359092
Sankaranarayanan et al. (1999)23India13519665
Chirenge et al. (1999)25Zimbabwe21487764
Denny et al. (1999)26South Africa29446584
Belinson et al. (2002)27China19977174
Denny et al. (2002)28South Africa27547379
Cronje et al. (2003)29South Africa10937949

Sanakarayanana et al.23 published data on 3000 women who were screened by paramedical personnel using DVI and cytology. The screeners were trained to grade the acetowhite lesions: the test was considered positive if any distinct acetowhite area was detected. If the acetowhitening was doubtful or faint, the test was scored as negative. DVI was considered positive in 9.8% of women compared with 10.2% with positive cytology (defined as atypia or worse). DVI detected 90.1% of the true positive cases (defined as histologically confirmed CIN 2 or worse) compared with cytology, which identified 86.2% of the true positives. The approximate specificities of DVI and cytology (just over 90%) were similar as were the PPVs (around 17%). In their study, cytology and DVI performed more or less equivalently as screening tests.

The University of Zimbabwe/JHPIEGO Cervical Cancer Project25 screened 10,934 women in two phases (8731 in phase 1 and 2203 in phase 2) using DVI and cytology. In phase 1 of the study, 18.1% of women had colposcopy based on a positive DVI or Pap smear. In the second phase of the study, 2147 (97.5%) of the 2203 women underwent colposcopy irrespective of the findings on DVI or cytology. The detection rate of CIN by DVI was similar to cytology and in phase 2 of the study, the sensitivity of DVI for HSIL or greater at 77% was higher than the sensitivity of cytology at 44%. The specificity of DVI for HSIL or greater, however, was 64% compared with 91% for cytology.

Denny et al.26 screened 2944 previously unscreened women, aged 35–65 years with conventional cytology, HPV DNA testing, DVI and cervicography. DVI was positive in 18% of the cases and identified 67% of all cases of high grade cervical disease, compared with cytology that identified 8% of women as having a positive test (CIN 1 or LSIL and greater) and identified 78% of the cases of high grade disease. This difference was not statistically different.

In another study, Denny et al.28 screened 2754 previously unscreened women aged 35–65 years using DVI with and without magnification. In addition, the screeners were trained to differentiate between different types of acetowhite lesions e.g. suspicious for cancer, a definite acetowhite lesion with a well-circumscribed border, non-confluent scattered lesions, an ill-defined lesion with poorly circumscribed borders and faintly acetowhite or no lesion visible at all. The estimated sensitivity of DVI when performed without magnification for high grade cervical cancer precursors was 70% compared with 74% when magnification was used, which was not statistically different. Restricting the definition of a positive DVI test to only a well-defined acetowhite lesion significantly reduced sensitivity of DVI for high grade cervical lesions to 58%.

In addition, this study evaluated the impact of concomitant sexually transmitted infections of the lower genital tract (culture proven Trichomonas vaginalis, molecular testing for Chlamydia trachomatis and Neisseria gonorrhoeae and HIV testing) and showed that the performance of DVI did not vary according to the presence of infection by these organisms, except for HIV-positive women in which the specificity of DVI was significantly reduced.

Sankaranarayanan et al.30 conducted a cluster randomised controlled intervention trial designed to evaluate the efficacy of a single round of DVI screening, provided by nurses, in reducing the incidence of and mortality from cervical cancer. In a preliminary report of their results, 48,225 women aged 30–59 years were randomised to DVI screening and 30,167 women were randomised to the control group (same age range) who were given education on cervical cancer and advised on how to access cervical cancer prevention services from local clinics and the hospital. No active intervention was provided to the control group and only 1.7% of these women availed themselves of screening services.

Of women eligible for the intervention group 63% were screened with DVI, and 10% of the women were DVI positive, all of whom underwent a colposcopic examination and 95% (n= 2777) underwent biopsy. The final diagnosis of CIN 1 was made in 1778 women, 222 had CIN 2/3 and 69 had screen-detected cancers. The programme sensitivity (i.e. during the follow up period) for the detection of cancer was 71% and the PPV for the detection of CIN 2/3 and cancer was 9%. Of note, seven out of 27,638 DVI-negative women were diagnosed with invasive cervical cancer within one to two years of screening, yielding a provisional longitudinal false-negative rate of 0.03%, which the authors found reassuring. In addition, the majority of screen detected cancers in women under 40 years were in stage I, indicating the ability of DVI and colposcopy to detect early preclinical cervical cancers.

Another important finding from this study was that of the women who requested not to be treated at the screening visit for a variety of reasons, only 47% finally returned for treatment. In addition, only 25% of the women treated for CIN at the screening visit returned for their follow up visit one year later. These poor return rates emphasise the potential value of linking screening with immediate treatment to prevent loss to follow up, which is inevitable in all laboratory-based screening tests where women are required to return for their results. In the study by Denny et al.,26 follow up rates of 95% were achieved if women were requested to return within two to six days of treatment and this rate fell to 85% if the result of the test (in this case, cytology) was delayed by two weeks.

DVI has several potential advantages for poorly resourced countries. Chief among these is the simplicity of the test, its low cost, the fact that primary health care providers can be trained in a relatively short period to perform the test and that an immediate result is provided.23 A disadvantage of DVI as a screening test is the difficulty of standardising quality control, which is particularly important considering the subjective nature of the test.

Linking DVI to immediate treatment in a primary care setting, which is often referred to as ‘screen and treat’, would eliminate many of the intermediate steps required for cytology-based screening protocols. However, the low specificity and low PPV of DVI observed in most clinical studies means that large numbers of women without disease would undergo treatment if all women with a positive DVI test result were offered immediate treatment. Although this is less advantageous than using a test with a high PPV, the actual negative impact of the expected over-treatment of women might be considerably less than previously thought. Recently, the results of a large ‘screen-and-treat’ programme that combined DVI with immediate treatment of all screen-positive women was reported from Thailand. Although the study did not evaluate the efficacy of this approach, it did evaluate safety and acceptability. Not a single serious complication of cryotherapy was observed among 756 women who underwent cryotherapy. In addition, 95% of women who participated in the programme expressed satisfaction with their experience.31

HPV DNA testing

  1. Top of page
  2. Abstract
  3. Introduction
  4. Primary prevention
  5. Clinical trials of prophylactic HPV vaccines
  6. Secondary prevention of cervical cancer
  7. What are the barriers to cervical cancer screening in developing countries?
  8. Visual inspection screening methods
  9. Direct visual inspection
  10. HPV DNA testing
  11. HPV DNA testing methods
  12. HPV DNA testing as a primary screening test
  13. Two-stage screening
  14. Self-testing for high risk types of HPV DNA
  15. Conclusions
  16. References

As has been pointed out, it is now widely accepted that persistent infection of the cervix with high risk types of HPV is necessary for the development of cervical cancer.3 This information has important implications for screening programmes, as it suggests that HPV DNA testing may be a viable alternative to cytological screening. It is particularly important in low resource settings that have not yet invested in developing cytologically based screening programmes. When considering the use of HPV DNA testing for primary screening in low resource settings, it is important to recognise that there are a number of issues that need to be dealt with before it can be widely adopted. Currently, the most widely ustilised HPV test [Hybrid Capture 2 (HC2), Digene, Gaithersburg, Maryland, USA] costs approximately US$30 per test, which is beyond the reach of most developing countries.

The second issue is the natural history of HPV infections. Anogenital HPV infections are very common in young, sexually active populations.32 In some studies, up to 70% of college-aged women are found to be HPV DNA positive.32–34 Fortunately, the majority of HPV infections in young women are transient, and only a minority of HPV-infected women develop persistent infections.32,34–37 It is only this small proportion of women who become persistently infected who are at risk for the subsequent development of CIN 2, 3 or cervical cancer. Therefore, if HPV DNA testing is to prove useful for primary cervical cancer screening, strategies need to be developed that avoid identifying large numbers of women with transient infections and focus on identifying those women with persistent infection. Transient HPV infections are much less common in women over the age of 30 years than among younger women and the HPV DNA positivity rate drops considerably after the age of 30 years.34 Therefore, one of the easiest ways not to identify large numbers of transiently infected women is to restrict screening to women 30 years of age and older. This is not a disadvantage for most developing countries that lack the resources to screen young women. Numerous cost-effectiveness studies have clearly shown that in settings where only one to three screens can be performed in a woman's lifetime, screening should not be initiated before the age of 30–35 years.

HPV DNA testing has a number of advantages as a screening test compared with either cervical cytology or DVI. The first is its higher sensitivity. A high sensitivity is particularly important in settings where women will be screened only once or twice in their lifetimes. The second is that HPV DNA testing not only identifies those women with concurrent cervical disease, but it also identifies those women at risk for developing cervical neoplasia within the next 3–10 years.38 This is particularly important for developing countries that might not have sufficient resources to screen all women at 5- to 10-year intervals but might have the resources to screen a small subset of high risk HPV DNA-positive women at more frequent intervals. The final advantage of HPV DNA testing is that the interpretation of the test is objective and does not have the inherent subjectivity of either visual screening methods or cervical cytology.

There are a number of ways in which HPV DNA testing could be incorporated into screening programmes, which include the following:

  • as a primary screening test
  • as part of a two-stage screening algorithm
  • self-collected specimens for detection of HPV DNA

HPV DNA testing methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Primary prevention
  5. Clinical trials of prophylactic HPV vaccines
  6. Secondary prevention of cervical cancer
  7. What are the barriers to cervical cancer screening in developing countries?
  8. Visual inspection screening methods
  9. Direct visual inspection
  10. HPV DNA testing
  11. HPV DNA testing methods
  12. HPV DNA testing as a primary screening test
  13. Two-stage screening
  14. Self-testing for high risk types of HPV DNA
  15. Conclusions
  16. References

The most widely used, commercially available, HPV DNA testing method is HC2 (Digene, Gaithersburg, Maryland, USA). This test uses two separate probe mixtures to identify either low risk types of HPV (6, 11, 42, 43 and 44) or high risk types of HPV (16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59 and 68). In terms of the infrastructure available in many developing countries, HC2 is a relatively technologically sophisticated and expensive test. However, compared with cervical cytology, HC2 requires considerably less training for technicians and has a higher throughput. Another advantage of HC2 is that the test has built-in quality control and is robust and reproducible.39,40

At the present time, considerable efforts are being made to develop a simpler and rapid HPV DNA test. If developed, these methods would allow the HPV DNA testing to be performed at district level laboratories or in health clinics in developing countries. When such tests become available, the possibility of screening women with HPV DNA testing and treating those with a positive test at the same visit may become a feasible alternative to cytology and colposcopy.

HPV DNA testing as a primary screening test

  1. Top of page
  2. Abstract
  3. Introduction
  4. Primary prevention
  5. Clinical trials of prophylactic HPV vaccines
  6. Secondary prevention of cervical cancer
  7. What are the barriers to cervical cancer screening in developing countries?
  8. Visual inspection screening methods
  9. Direct visual inspection
  10. HPV DNA testing
  11. HPV DNA testing methods
  12. HPV DNA testing as a primary screening test
  13. Two-stage screening
  14. Self-testing for high risk types of HPV DNA
  15. Conclusions
  16. References

A number of studies have evaluated the use of HPV DNA testing as a primary screening test (Table 2). These studies have included significant numbers of women and have been conducted in areas of the world with high prevalence of cervical cancer such as Mexico, Costa Rica, South Africa and China.41–44 In these studies a consistently greater sensitivity for the detection of CIN 2, 3 or greater lesions has been observed using HPV DNA testing for high risk types of HPV compared with cytology. However, the specificity of HPV DNA testing has been somewhat lower than that of cytology in most of these different studies, except for that of Beilinson et al.44 from China, which reported a very high sensitivity for cytology that was accompanied by a very low specificity.

Table 2.  Performance of cervical cytology and HC2 HPV testing for screening in women 30 years of age and older in cross-sectional studies.
Populationn% CIN 2+Sensitivity (%)Specificity (%)
CytologyHPVCytologyHPV
Mexico4161151.4157.094.298.894.0
Costa Rica4261761.7580.486.394.594.4
South Africa4329253.5674.084.987.981.8
China4419364.3494.097.677.884.8

In the context of screening, good sensitivity (i.e. the ability of the test to detect all women with the condition of interest) has to be balanced against the test's specificity. Specificity is particularly important in cervical cancer screening because screening involves large numbers of otherwise healthy women, and positive screening test results require a follow up colposcopic evaluation that is both uncomfortable and costly. Specificity takes on added importance in low resource settings where colposcopy is not available and all women who are classified as screening test positive would be treated in a ‘screen-and-treat’ approach.

One of the advantages of HPV DNA testing in these settings is that the specificity of the test can be altered by adjusting the cutoff level used to define a positive result or by altering the number of high risk HPV types that are detected by the screening test. Our Cape Town data indicate that if we were willing to arbitrarily set the number of women with cervical disease who are classified as screening test positive at 10%, testing for high risk HPV DNA using HC2 would detect 79% of all cases of CIN 2, 3 or cancer. However, the threshold for classifying women without CIN 2, 3 or cancer as being screening test positive was dropped to 5%, then either HC2 or Hybrid Capture I would identify only 57% of the cases of CIN 2, 3 or cancer.43 Currently, we are evaluating the potential impact that modifying the number of high risk HPV types that are tested for would have in our Cape Town population. We are doing this by identifying the specific types of HPV that are present in women within different disease categories and then calculating the potential sensitivity and specificity of testing for specific combinations of HPV.

Two-stage screening

  1. Top of page
  2. Abstract
  3. Introduction
  4. Primary prevention
  5. Clinical trials of prophylactic HPV vaccines
  6. Secondary prevention of cervical cancer
  7. What are the barriers to cervical cancer screening in developing countries?
  8. Visual inspection screening methods
  9. Direct visual inspection
  10. HPV DNA testing
  11. HPV DNA testing methods
  12. HPV DNA testing as a primary screening test
  13. Two-stage screening
  14. Self-testing for high risk types of HPV DNA
  15. Conclusions
  16. References

An alternative approach to the use of HPV DNA testing alone as a primary screening test would be to utilise the test together with another test to sequentially screen women in a ‘two-stage’ approach. With this approach, all women would be initially screened using a relatively non-specific screening test, such as DVI or HPV DNA testing and only women with a positive initial screening test would be re-screened using a second test that could either be HPV DNA testing, DVI or cytology. Only women found to be positive on both screening tests would be referred for evaluation or treated if a ‘screen-and-treat’ approach were being utilised.

In the Cape Town study we evaluated the performance of a ‘two-stage’ screening approach using combinations of HPV DNA testing, cytology, DVI and cervicography.45 Assuming that a ‘screen-and-treat’ approach was used in which all women who were classified as positive underwent immediate treatment, we found that if DVI alone were used for screening, 21% of all screened women would be treated and only 12% of those treated would have CIN 2, 3 or cancer. This approach would identify 21 cases of cervical disease per 1000 women screened. If a ‘two-stage’ screening approach were used in which DVI was the first test, followed by conventional cytology, only 4% of the population screened would be classified as being ‘positive’ and require treatment, of whom 55% would have CIN 2, 3 or cancer. Eighteen cases of cervical disease per 1000 women screened would be identified. Similarly, a ‘two-stage’ screening protocol using DVI followed by HPV DNA testing would classify 6% of screened women as positive and would identify 16 cases of cervical disease per 1000 women screened.

The advantage of the ‘two-stage’ approach to screening is that it would greatly reduce the number of women classified as screening test positive. However, the disadvantage is that it produces a smaller, but in many cases significant, reduction in sensitivity. Depending on its magnitude, this reduction might be detrimental in low resource settings where women might be expected to have access to the screening test only once or twice in their lifetime.

Self-testing for high risk types of HPV DNA

  1. Top of page
  2. Abstract
  3. Introduction
  4. Primary prevention
  5. Clinical trials of prophylactic HPV vaccines
  6. Secondary prevention of cervical cancer
  7. What are the barriers to cervical cancer screening in developing countries?
  8. Visual inspection screening methods
  9. Direct visual inspection
  10. HPV DNA testing
  11. HPV DNA testing methods
  12. HPV DNA testing as a primary screening test
  13. Two-stage screening
  14. Self-testing for high risk types of HPV DNA
  15. Conclusions
  16. References

One way in which HPV DNA testing could be utilised to screen large numbers of women without access to speculum examinations is through the use of self-collected vaginal samples. Previously we published data on supervised self-testing for high risk types HPV DNA in our cohort of South African women.46 The sensitivity of HPV DNA testing of a self-collected vaginal sample for CIN 2, 3 or cancer was 66% (95% CI: 52–78%), which was equivalent to that of the conventional cervical smear when LSIL or greater was defined as a positive test (61%; 95% CI: 47–73%, P= 0.58). In contrast, the sensitivity of HPV DNA testing of a clinician obtained sample was 84% (95% CI: 71–92%), which was significantly greater than the sensitivity of a conventional cervical smear and of a self-collected sample for HPV DNA testing.

These data suggest that in settings where cytology screening is not available, self-collected HPV DNA testing may be useful for identifying older women at risk for cervical disease. The limitations of this approach however need to be appreciated, particularly the lower sensitivity for high grade lesions compared with a clinician obtained sample and the lower specificity than cytology. The use of self-collected samples could provide a potential opportunity to extend cervical cancer screening to large numbers of unscreened women, particularly women who are resistant to undergoing a speculum examination or have poor access to health care facilities.

Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Primary prevention
  5. Clinical trials of prophylactic HPV vaccines
  6. Secondary prevention of cervical cancer
  7. What are the barriers to cervical cancer screening in developing countries?
  8. Visual inspection screening methods
  9. Direct visual inspection
  10. HPV DNA testing
  11. HPV DNA testing methods
  12. HPV DNA testing as a primary screening test
  13. Two-stage screening
  14. Self-testing for high risk types of HPV DNA
  15. Conclusions
  16. References

While the development of a prophylactic HPV vaccine may be the ultimate solution to the prevention of cervical cancer, it is unlikely that the vaccine will be widely available in low resource settings with the next decade. In the meantime large numbers of women already infected with high risk types of HPV remain at risk of developing cervical cancer. Therefore, despite the potential that vaccines offer for reducing death from cervical cancer, it is imperative to continue to develop a technologically appropriate, accessible and effective alternative to the current cytologically based approach to cervical cancer prevention.

There are currently a number of randomised clinical trials evaluating ‘screen-and-treat’ approaches using both DVI and HPV testing. The results of these trials should provide high quality evidence of the impact of these approaches on the prevention of cervical cancer.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Primary prevention
  5. Clinical trials of prophylactic HPV vaccines
  6. Secondary prevention of cervical cancer
  7. What are the barriers to cervical cancer screening in developing countries?
  8. Visual inspection screening methods
  9. Direct visual inspection
  10. HPV DNA testing
  11. HPV DNA testing methods
  12. HPV DNA testing as a primary screening test
  13. Two-stage screening
  14. Self-testing for high risk types of HPV DNA
  15. Conclusions
  16. References
  • 1
    Ferlay J, Bray F, Pisawi P, Parkin DM. GLOBOCAN 2000. Cancer Incidence, Mortality and Prevalence Worldwide. Version 1.0. IARC Cancer Base No. 5. Lyon: IARC Press, 2001.
  • 2
    ParkinDM, WhelanSL, FerlayJ, TeppoL, ThomasDB, editors. Cancer Incidence in Five Continents, VIII. IARC Scientific Publications No. 155, Lyon, France: International Agency for Research on Cancer, 2002.
  • 3
    Walboomers JM, Jacobs MV, Manos MM, et al. Human papillomavirus is a necessary cause of invasive cervical cancer world wide. J Pathol 1999;189: 1219.
  • 4
    Munoz N, Bosch FX, de Sanjose S, et al. Epidemiologic classification of human papillomavirus types associated with cervical cancer. N Engl J Med 2003;348: 518527.
  • 5
    Clifford GM, Smith JS, Plummer M, Munoz N, Franceschi S. Human papillomavirus types in invasive cervical cancer worldwide: a meta-analysis. Br J Cancer 2003;88: 6373.
  • 6
    Christensen ND, Kreider JW, Cladel NM, Patrick SD, Welsh PA. Monoclonal antibody-mediated neutralization of infectious human papillomavirus type 11. J Virol 1990;64: 56785681.
  • 7
    Schwarz E, Freese UK, Gissmann L, et al. Structure and transcription of human papillomavirus sequences in cervical carcinoma cells. Nature 1985;314: 111114.
  • 8
    Bontkes HJ, DeGruijl TD, Walboomers JMM, et al. Immune responses against human papillomavirus (HPV) type 16 virus like particles in a cohort study of women with cervical intraepithelial neoplasia II. Systemic but not local IGA responses correlate with clearance of HPV16. J Gen Virol 1999;80: 409417.
  • 9
    Kirnbauer R, Booy F, Cheng N, Lowy DR, Schiller JT. Papillomavirus L1 major capsid protein self-assembles into virus-like-particles that are highly immunogenic. Proc Natl Acad Sci U S A 1992;89: 1218012184.
  • 10
    Harro CD, Pang YY, Roden RB, et al. Safety and immunogenicity trial in adult volunteers of a human papillomavirus 16 L1 virus-like-particle vaccine. J Natl Cancer Inst 2001;93: 284292.
  • 11
    Koutsky LA, Ault KA, Wheeler CM, et al. A controlled trial of a human papillomavirus type 16 vaccine. N Engl J Med 2002;347: 16451647.
  • 12
    Harper DM, Franco EL, Wheeler C, et al. Efficacy of a bivalent L1 virus-like particle vaccine in prevention of infection with human papillomavirus types 16 and 18 in young women: a randomised controlled trial. Lancet 2004;364: 17571764.
  • 13
    Summary chapter: IARC Working Group on Cervical Cancer Screening. In: HakamaM, MillerAB, DayNE, editors. Screening for Cancer of the Uterine Cervix. Lyon: International Agency for Research on Cancer, 1986: 133142.
  • 14
    IARC Working Group on Evaluation of Cervical Cancer Screening Programmes. Screening for squamous cervical cancer: the duration of low risk after negative result of cervical cytology and its implication for screening policies. BMJ 1986;293: 659664.
  • 15
    Hakama M, Louhivuori K. A screening programme for cervical cancer that worked. Cancer Surv 1988;17(3):403416.
  • 16
    Howson C, Harrison P, Hotra D, Law M. In Her Lifetime. Female Morbidity and Mortality in Sub-Saharan Africa. Washington (DC): National Academy Press, 1996: 2553 [Chapter 2].
  • 17
    Nanda K, McCrory DC, Myers ER, et al. Accuracy of the Papanicolaou test in screening for and follow-up of cervical cytologic abnormalities: a systematic review. Ann Intern Med 2000;132: 810819.
  • 18
    Fahey MT, Irwig L, Macaskill P. Meta-analysis of Pap test accuracy. Am J Epidemiol 1995;141: 680689.
  • 19
    Schiller W. Leucoplakia, leucokeratosis, and carcinoma of the cervix. Am J Obstet Gynecol 1938;35: 1738.
  • 20
    Ottaviano M, La Torre P. Examination of the cervix with the naked eye using acetic acid test. Am J Obstet Gynecol 1982;143: 139142.
  • 21
    Cecchini S, Bonardi R, Mazzotta A, Grazzini G, Iossa A, Ciatto S. Testing cervicography and cervicoscopy as screening tests for cervical cancer. Tumori 1993;79: 2225.
  • 22
    Megevand E, Denny L, Dehaeck K, Soeters R, Bloch B. Acetic acid visualization of the cervix: an alternative to cytologic screening. Obstet Gynecol 1996;88: 383386.
  • 23
    Sankaranarayanan R, Shyamalakumary B, Wesley R, Sreedevi Amma N, Parkin DM, Nair MK. Visual inspection with acetic acid in the early detection of cervical cancer and precursors. Int J Cancer 1999;80: 161163.
  • 24
    Sankaranarayanan R, Wesley R, Somanathan T, et al. Visual inspection of the uterine cervix after the application of acetic acid in the detection of cervical carcinoma and its precursors. Cancer 1998;83: 21502156.
  • 25
    University of Zimbabwe/JHPIEGO Cervical Cancer Project. Visual inspection with acetic acid for cervical-cancer screening: test qualities in a primary-care setting. Lancet 1999;353: 869873.
  • 26
    Denny L, Kuhn L, Pollack A, Wainwright H, Wright Jr TC. Evaluation of alternative methods of cervical cancer screening for resource-poor settings. Cancer 2000;89: 826833.
  • 27
    Belinson JL, Pretorius RG, Zhang WH, Wu LY, Qiao YL, Elson P. Cervical cancer screening by simple visual inspection after acetic acid. Obstet Gynecol 2001;98: 441444.
  • 28
    Denny L, Kuhn L, Pollack A, Wright Jr TC. Direct visual inspection for cervical cancer screening. An analysis of factors influencing test performance. Cancer 2002;94: 16991707.
  • 29
    Cronje H, Parham G, Cooreman B, de Beer A, Divall P, Bam R. A comparison of four screening methods for cervical neoplasia in a developing country. Am J Obstet Gynecol 2003;183: 395400.
  • 30
    Sankaranayan R, Rajkumar R, Theresa R, et al. Initial results from a randomized trial of cervical visual screening in rural South India. Int J Cancer 2004;109: 461467.
  • 31
    Gaffikin L, Blumenthal P, Emerson M, et al. Safety, acceptability, and feasibility of a single visit approach to cervical-cancer prevention in rural Thailand: a demonstration project. Lancet 2003;361: 814820.
  • 32
    Ho GYF, Bierman R, Beardsley L, Chang CJ, Burk RD. Natural history of cervicovaginal papillomavirus infection in young women. N Engl J Med 1998;338: 423428.
  • 33
    Wheeler CM, Greer CE, Becker TM, Hunt WC, Anderson SM, Manos MM. Short-term fluctuations in the detection of cervical human papillomavirus DNA. Obstet Gynecol 1996;88: 261268.
  • 34
    Cuzick J, Sasieni P, Davies P, et al. A systematic review of the role of human papillomavirus testing within a cervical screening programme. Health Technol Asses 1999;3(14):6162.
  • 35
    Hildesheim A, Schiffman MH, Gravitt PE, et al. Persistence of type-specific human papillomavirus infection among cytologically normal women. J Infect Dis 1994;169: 235240.
  • 36
    Evander M, Edlund K, Gustafsson A, et al. Human papillomavirus infection is transient in young women: a population-based cohort study. J Infect Dis 1995;171: 10261030.
  • 37
    Moscicki AB, Palefsky JM, Smith G, Siboshski S, Schoolnik G. Variability of human papillomavirus DNA testing in a longitudinal cohort of young women. Obstet Gynecol 1993;82: 578585.
  • 38
    Koutsky LA, Holmes KK, Critchlow CW, et al. A cohort study of the risk of cervical intraepithelial neoplasia grade 2 or 3 in relation to papillomavirus infection. N Engl J Med 1992;327(18):12721278.
  • 39
    Schiffman MH, Kiviat NB, Burk RD, et al. Accuracy and interlaboratory reliability of human papillomavirus DNA testing by hybrid capture. J Clin Microbiol 1995;33: 545550.
  • 40
    Castle PE, Lorincz AT, Mielzynska-Lohnas I, et al. Results of human papillomavirus DNA testing with the Hybrid Capture 2 assay are reproducible. J Clin Microbiol 2002: 10881090 (March).
  • 41
    Salmeron J, Lazcano-Ponce E, Lorincz A, Hernandez M, Hernandez P, Leyva A. Comparison of HPV-based assays with Papanicolaou smears for cervical cancer screening in Morelos State, Mexico. Cancer Causes Control 2003;14(6):505515.
  • 42
    Schiffman M, Herrero R, Hildesheim A, et al. HPV DNA testing in cervical cancer screening: results from a high-risk province in Costa Rica. JAMA 2000;283: 8793.
  • 43
    Kuhn L, Denny L, Pollack A, Wright TC. Human papillomavirus DNA testing for cervical cancer screening in low-resource settings. J Natl Cancer Inst 2000;92: 818825.
  • 44
    Belinson J, Qiao Y, Pretorius R, et al. Prevalence of cervical cancer and feasibility of screening in rural China: a pilot study for the Shanxi province cervical cancer screening study. Int J Gyn Cancer 1999;9: 411417.
  • 45
    Denny L, Kuhn L, Risi L, et al. Two-stage cervical cancer screening: an alternative for resource-poor settings. Am J Obstet Gynecol 2000;183: 383388.
  • 46
    Wright TC, Denny L, Kuhn L, Pollack A, Lorincz A. HPV DNA testing of self-collected vaginal samples compared with cytologic screening to detect cervical cancer. JAMA 2000;283: 8186.