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Keywords:

  • mesothelioma;
  • effusion;
  • cytology;
  • pleura;
  • fluid

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. FUNDING SOURCES
  7. CONFLICT OF INTEREST DISCLOSURE
  8. REFERENCES

BACKGROUND

The diagnosis of malignant mesothelioma (MM) in effusion specimens is controversial. At the study institution (Northwestern University), a primary diagnosis of MM is made on fluid cytology specimens. In an effort to estimate the practice at other institutions, a survey was disseminated regarding cytologic diagnosis of MM. The authors also evaluated their own institution's experience with primary cytologic diagnosis of MM.

METHODS

Patients with MM at the study institution were identified from 1992 through 2011. Fluid cytology specimens preceding histologic diagnoses were reviewed. A survey was sent to a number of cytology laboratories to assess practice patterns regarding the diagnosis of MM.

RESULTS

At the study institution, 20 cases of MM had effusion specimens preceding the diagnostic histologic material. In 6 cases (30%), a definitive diagnosis of MM was rendered via cytology alone. There were no false-positive diagnoses of MM. Of 55 laboratories that responded to the survey, 36 reported making a definitive diagnosis of MM after cytologic analysis. Almost all laboratories (35) willing to diagnose MM in effusions reported performing immunohistochemistry to distinguish adenocarcinoma from MM. A smaller proportion (18) of these laboratories reported doing additional immunohistochemistry or fluorescence in situ hybridization for p16 to help distinguish benign from malignant mesothelial proliferations. Those who do not definitively diagnose MM in fluid specimens state inability to identify invasion and overlap with reactive mesothelial proliferation as factors supporting their practice. Most respondents (32) felt that the clinicians at their institution would manage a patient based on a cytologic diagnosis of MM.

CONCLUSIONS

The majority of respondents reported making a definitive diagnosis of MM in effusion cytology specimens. The diagnosis of MM in effusions, although not sensitive, is extremely specific. Cancer (Cancer Cytopathol) 2013;121:703–707. © 2013 American Cancer Society.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. FUNDING SOURCES
  7. CONFLICT OF INTEREST DISCLOSURE
  8. REFERENCES

A diagnosis of malignant mesothelioma (MM) carries grave implications due to an almost universally fatal disease course. Despite an increase in incidence in the last several decades, MM is still a relatively rare disease and most pathologists do not accrue substantial experience with this entity outside of large academic centers. Although radiographic and clinical findings may be highly suggestive, definitive diagnosis and therapy traditionally rely on histopathologic evaluation of pleural, pericardial, or peritoneal biopsies.

The histomorphologic criteria of MM have been well documented in recent consensus statements as well as in the WHO “Blue Book.”[1, 2] Key features of mesothelioma include complex architectural arrangements, necrosis, and an expansile and disorganized growth pattern. Regardless of the presence or absence of these features in a small tissue biopsy, most surgical pathologists will demur from a definitive diagnosis of MM without identifiable stromal invasion and clear-cut involvement of fat or skeletal muscle.

Perhaps because of the weight placed on this single architectural feature, effusion cytology has historically not been accepted as an adequate specimen type for definitive diagnosis of MM. As such, the most recent consensus statement from the International Mesothelioma Interest Group states that “there is limited usefulness of cytology, histochemical stains, and electron microscopy.”[1]

Although reservations regarding the definitive diagnosis of this disease are understandable, the cytologic features of MM in fluid specimens are well documented. Key among cytologic criteria for MM in the differential diagnosis with reactive mesothelial hyperplasia are macronucleoli and large cell clusters[3, 4] (Figs. 1 and 2). Immunohistochemistry (IHC) is of limited value in this setting; however, recent publications have documented the utility of fluorescence in situ hybridization (FISH), which can demonstrate a deletion in p16 in approximately 60% of cases of MM with 100% specificity.[5] In a frankly malignant effusion, cell groups with knobby borders, low nuclear:cytoplasmic ratios, lack of pleomorphism, and dense cytoplasm all suggest MM as opposed to adenocarcinoma. The utility of IHC analysis to confirm mesothelial origin and exclude adenocarcinoma in this scenario is well documented.[6]

image

Figure 1. Malignant mesothelioma in pleural fluid (Papanicolaou stain, magnification ×10) is shown. Note the cellular effusion with a single cell population and large clusters of epithelioid cells with knobby borders (“morulae”).

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image

Figure 2. Malignant mesothelioma in pleural fluid (hematoxylin and eosin cell block, magnification ×40) is shown. The large clusters of cells display a mesothelial phenotype (cell wrapping, low nuclear:cytoplasmic ratios, knobby cell group borders). The large cell group and occasional macronucleoli are suggestive of malignant mesothelioma.

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In order to explore actual practice patterns in regard to the definitive diagnosis of MM in effusion cytology, we constructed and distributed an Internet-based survey to evaluate institutional experience at several dozen cytopathology divisions, both academic and nonacademic. In addition, we evaluated our own experience and reviewed the recent English-language literature relating to this topic.

MATERIALS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. FUNDING SOURCES
  7. CONFLICT OF INTEREST DISCLOSURE
  8. REFERENCES

We constructed an Internet-based survey designed to assess practice patterns in the diagnosis of MM in cytologic material. The language of the survey was specifically designed to query issues relating to the willingness of pathologists to unequivocally diagnose MM in effusion cytology specimens, the use of ancillary studies in this context, and perceived clinician acceptance of a cytologic diagnosis of MM. Pathologists at 68 institutions were invited to participate in the survey.

In addition, we reviewed the effusion cytology slides and reports of 20 histologically confirmed cases of MM from the preceding 11 years at Northwestern Memorial Hospital (Chicago, Ill).

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. FUNDING SOURCES
  7. CONFLICT OF INTEREST DISCLOSURE
  8. REFERENCES

We received responses from 55 of the 68 surveyed institutions. Forty-five of the received surveys were returned by academic institutions, with community hospitals (7), military institutions (2), and reference laboratories (1) accounting for the remainder. The volume of “positive for malignant mesothelioma” and “suspicious for malignant mesothelioma” cases varied from fewer than 5 in the last 10 years (10% of respondents) to more than 50 (25% of respondents).

Of the respondents, 35 (63%) replied that they do make a definitive diagnosis of MM in effusion material. The vast majority of this group (94%) stated that they will do so in the context of both a primary diagnosis and recurrence. The most commonly cited feature useful in making a diagnosis was architectural atypia in the form of large groups of mesothelial cells with knobby borders. The next most commonly cited features were high cellularity in effusions composed of mesothelial cells and effusions containing mesothelial cells with marked cytologic atypia.

Among respondents who did not make a definitive diagnosis of MM in effusions, the most commonly cited reasons were an inability to assess stromal invasion and minimal cytologic atypia.

In cases where MM is suspected in a frankly malignant effusion, all respondents reported using a panel of IHC stains to rule out adenocarcinoma. Slightly more than half (55%) reported using ancillary studies (ie, FISH, IHC) to support malignancy in the context of an atypical mesothelial proliferation.

Of the pathologists who responded to our survey, 32 (63%) felt that the clinicians at their institution would treat a patient definitively based on a cytologic diagnosis of MM. This question addressed diagnoses based on both fine-needle aspiration (FNA) specimens as well as effusion specimens without distinction.

We reviewed the medical records of patients with histologically confirmed peritoneal and pleural MM from 2002 through 2011 at Northwestern Memorial Hospital. We identified 20 cases that had a fluid cytology specimen within the 3 months prior to histologic confirmation. Of these 20 cases, 6 (30%) received a cytologic diagnosis of “Positive for malignant mesothelioma” at the time of service based on the cytomorphologic, clinical, and, in some cases, IHC findings. In addition, 6 cases were designated “atypical,” 2 were misclassified as “positive for adenocarcinoma,” 1 was “suspicious for mesothelioma,” and the remainder were classified as benign. There were no false-positive diagnoses of MM in effusion specimens during this time period.

Conclusions

Given the pronouncements of the WHO Blue Book and recent International Mesothelioma Interest Group consensus document, it is interesting to note that the majority of the respondents to our survey were comfortable making a definitive diagnosis of MM in effusion specimens. In arriving at this diagnosis, clinicopathologic correlation and the thoughtful integration of ancillary studies are critical.

The published literature supports the assertion that a cytologic diagnosis of MM supported by clinical data and ancillary studies, although marginal in regard to sensitivity, is extremely specific. Earlier work, much of it prior to the contemporary IHC and molecular paradigm, has documented the sensitivity of effusion cytology for MM to be between 32% and 76%.[7-10] It must be noted that the figures cited by most studies include both “Positive” as well as “Suspicious” results. If only definitive “Positive for mesothelioma” results are counted, as in our case review, the sensitivity is markedly lower. Although not specifically addressed in the prior studies, no instance of a false-positive diagnosis of mesothelioma was noted by any of the authors.

In a frankly malignant effusion where the clinical and/or morphologic features are suggestive of MM, nearly all respondents reported using a panel of IHC stains in order to prove or disprove mesothelial derivation. The utility of IHC in this context is well documented. Although no single stain is entirely sensitive or specific for MM, a panel of stains including both mesothelial (calretinin, WT1, d2-40) and epithelial (Moc31, BerEp4, CEA) markers can often be definitive in the differential diagnosis of adenocarcinoma and MM. Even a minimal 3-antibody panel has been shown to be 96% sensitive and specific in making this distinction.[11]

A smaller proportion of respondents (56%) reported using ancillary studies including IHC and FISH to establish malignancy in proliferations that are morphologically obviously mesothelial, but indeterminate in regard to malignancy. Whereas a number of traditional IHC markers have been evaluated for this purpose (EMA, p53, and desmin), none of them have demonstrated the degree of specificity required to establish an unequivocal diagnosis of MM. More recent work has focused on newer markers such as GLUT1, CD147, and IMP3.[12] Although initial reports of the performance characteristics of these antibodies were promising and demonstrated excellent sensitivity and specificity, more recent publications have failed to confirm these results. It would appear that more data is required before a definitive statement of the utility of these newer IHC markers can be made.

FISH, in contrast, is rapidly emerging as an extremely useful confirmatory tool in the diagnosis of MM. A recent study performed on effusion specimens focused on the evaluation of p16 deletions on chromosome 9 found that 59% of MMs, including 70% of pleural mesotheliomas, demonstrated homozygous p16 deletions. In line with prior work, this study demonstrated the absolute (100%) specificity of a p16 deletion for MM in a mesothelial proliferation.[5] Notably, cytogenetic abnormalities, including homozygous p16 deletions, may be seen in other malignancies as well. As such, it is important to confirm that a proliferation is mesothelial in nature when interpreting FISH results.

The majority (63%) of cytopathologists who responded to our survey felt that the clinicians at their institution would definitively manage a patient on the basis of a positive cytology result. The question specifically referenced both FNA as well as effusion cytology without distinction. An unequivocal diagnosis of MM is useful for therapeutic purposes in many cases, because it expedites therapy and theoretically may avoid seeding of an incision or biopsy site by the tumor. One caveat to the diagnosis of MM via cytology is that there is, as of yet, no reliable way to distinguish the epithelioid, sarcomatoid, and biphasic variants. Although many patients are unresectable at the time of presentation, knowledge of histologic subtype is critical in patients who may clinically be surgical candidates[14] in that a significant sarcomatoid component is considered a contraindication to resection at most centers. Therefore, even with a definitive cytologic diagnosis of mesothelioma and a clinician who accepts it as such, a tissue specimen may still often be necessary to determine subtype.

In conclusion, the results of our survey indicate that a majority of respondents will issue a definitive diagnosis of MM in effusion specimens. This practice appears to be supported by the literature, which documents the excellent specificity of a cytologic diagnosis of MM in the appropriate clinical setting and with supporting ancillary data. Most responding cytopathologists perceive the clinicians at their institution will manage a patient based solely upon a cytologic diagnosis (FNA and/or effusion cytology). Limitations of effusion cytology in this context include a relatively low sensitivity when considering morphology alone as well as an inability to histologically subtype cases.

Table 1. Survey Questions
 
What is your practice setting? (n = 55)
Academic medical center: 45 (81%)
Community hospital: 7 (13%)
Military hospital: 2 (4%)
Reference laboratory: 1 (2%)
Do you make a definitive diagnosis of mesothelioma in cytologic specimens? (n = 55)
Yes: 36 (65%)
No: 19 (35%)
If yes, under what conditions will you make a definitive diagnosis of malignant mesothelioma? (n = 36)
Recurrence only: 2 (5%)
Primary diagnosis as well as recurrence: 34 (95%) (62% of all respondents)
If no, why not? (n = 13)
Too much morphologic overlap with reactive mesothelial cells: 6 (46%)
Inability to assess stromal invasion in cytologic specimens: 4 (31%)
Consensus with clinicians and surgical pathologists: 3 (23%)
In which specimen type will you make a definitive diagnosis of malignant mesothelioma? (n = 36)
Effusion + Cell Block only: 4 (11%) (9% of respondents)
Fine-Needle Aspirate + Cell Block only: 2 (6%)
Both: 30 (83%) (55% of all respondents)
Do you routinely perform immunohistochemistry (IHC) to support a diagnosis of malignant mesothelioma versus adenocarcinoma? (n = 37)
Yes: 35 (95%)
No: 2 (5%)
Do you perform additional IHC or fluorescence in situ hybridization to confirm malignant mesothelioma versus reactive mesothelial cells? (n = 32)
Yes: 18 (56%)
No: 14 (44%)
In an effusion specimen, which of these features do you find most concerning for malignant mesothelioma? (multiple responses possible, n = 34)
High cellularity of mesothelial cells: 16 (47%)
Monotonous population of cells without easily identifiable second population of benign mesothelial cells: 13 (38%)
Abnormally large clusters of mesothelial cells: 28 (82%)
Cytoplasmic density and staining quality: 5 (15%)
Cells with mesothelial morphology and marked cytologic atypia: 6 (18%)
Do you feel that clinicians at your institution will manage a patient on the basis of a cytologic (fine-needle aspirate or effusion cytology) diagnosis of malignant mesothelioma? (n = 51)
Yes: 32 (63%)
No: 19 (37%)
What is the approximate number of definite mesothelioma or suspicious for mesothelioma cases diagnosed by your laboratory in the past 10 years? (n = 48)
<5: 5 (10%)
5-15: 10 (21%)
16-30: 18 (38%)
31-50: 3 (6%)
>50: 12 (25%)

CONFLICT OF INTEREST DISCLOSURE

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. FUNDING SOURCES
  7. CONFLICT OF INTEREST DISCLOSURE
  8. REFERENCES

Dr. Nayar is an employee of Northwestern University, has received speakers fees from McGill University, and has received travel/meeting expenses from Northwestern and College of American Pathologists. All other authors made no disclosure.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. FUNDING SOURCES
  7. CONFLICT OF INTEREST DISCLOSURE
  8. REFERENCES
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  • 2
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    DiBonito L, Falconieri G, Colautti I, Bonifacio Gori D, Dudine S, Giarelli L. Cytopathology of malignant mesothelioma: a study of its patterns and histological bases. Diagn Cytopathol. 1993;9:25-31.
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    Sherman ME, Mark EJ. Effusion cytology in the diagnosis of malignant epithelioid and biphasic pleural mesothelioma. Arch Pathol Lab Med. 1990;114:845-851.
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    Yaziji H, Battifora H, Barry TS, et al. Evaluation of 12 antibodies for distinguishing epithelioid mesothelioma from adenocarcinoma: identification of a three-antibody immunohistochemical panel with maximal sensitivity and specificity. Mod Pathol. 2006;19:514-523.
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    Neragi-Miandoab S, Richards WG, Sugarbaker DJ. Morbidity, mortality, mean survival, and the impact of histology on survival after pleurectomy in 64 patients with malignant pleural mesothelioma. Int J Surg. 2008;6:293-297.