Breast fine-needle aspiration cytology performance in the high-risk screening population
A study of BRCA1/BRCA2 mutation carriers
The diagnosis of breast lesions is usually confirmed by fine-needle aspiration cytology (FNAC) or histological biopsy. Although there is increasing literature regarding the advantages and limitations of both modalities, there is no literature regarding the accuracy of these modalities for diagnosing breast lesions in high-risk patients, who usually have lesions detected by screening. The objective of the current study was to evaluate diagnostic performance indices of FNAC in breast cancer susceptibility gene (BRCA) mutation carriers.
BRCA1/BRCA2 mutation carriers who underwent FNAC were selected from the database of the Rotterdam Family Cancer Clinic. FNAC accuracy parameters were calculated by taking the outcome of a subsequent histological diagnosis or clinical follow-up as reference standard.
In total, 320 FNACs were obtained, and FNAC examination was followed by histological examination in 150 patients. The rate of insufficient material was 25.6%. Sensitivity was 92.3%, specificity 96.3%. The false-positive rate was 3.7%, the false-negative rate was 7.7%, and accuracy was 94.7%. A substantial proportion of patients (35%) with malignant FNAC results underwent histological biopsy upfront surgical resection. Small lesion size (≤1 cm) and nonpalpability of the breast lesion were associated with decreased FNAC accuracy. In 113 patients who had a benign FNAC outcome without histological follow-up, no malignancies were detected during clinical or radiologic surveillance (median follow-up 84 months).
There is a role for FNAC in diagnosing breast lesions of BRCA1/BRCA2 mutation carriers, ie, to confirm a radiological (probably) benign lesion. However, despite the high overall sensitivity of FNAC, the authors recommend histological biopsy as the preferred diagnostic method for high-risk patients who have small or nonpalpable lesions. Cancer (Cancer Cytopathol) 2013;121:561–567. © 2013 American Cancer Society.
Carriers of mutations in the breast cancer susceptibility genes BRCA1 and BRCA2 have a significantly greater lifetime risk of developing breast cancer compared with the general population. The increase in risk starts as early as age 25 years, and approximately 40% to 65% of these women have developed breast cancer by age 70 years. Because of this elevated risk, carriers are advised to start routine annual mammary screening with mammography and magnetic resonance imaging (MRI) at a young age.[1-3]
Screening with MRI is twice as sensitive as screening with mammography in BRCA1 and BRCA2 mutation carriers. However, the specificity of MRI is limited, which results in an increased detection rate of small, generally nonpalpable lesions and a subsequent increase in the number of diagnostic procedures. This obviously leads to the detection of cancer at an early stage, but at the expense of increased patient anxiety because of an increased detection rate of benign lesions.
Fine-needle aspiration cytology (FNAC) and core-needle biopsy (CNB) or vacuum-assisted biopsies (VAB) are used routinely for pathologic diagnosis, and both have their advantages and limitations. Overall, FNAC allows rapid diagnosis with limited morbidity and high success rates, especially in clinically/radiologically clearly benign and malignant lesions.[5-12] Important factors that influence the accuracy of FNAC are the experience of the aspirator and the cytopathologist. Moreover, the success rates of FNAC depend on clinical/radiologic features and are especially low for small, nonpalpable lesions.[8-10, 12, 13] Other limitations of FNAC include an inability to distinguish between in situ and invasive carcinoma, the diagnosis of several morphologic entities (papillary, fibroepithelial, and calcified lesions), and the dubious assessment of receptor status in case of malignancy.[6, 13] Several studies have concluded that CNB has higher sensitivity compared with FNAC. Sensitivity varies from 85% to 100% for CNB and from 35% to 95% for FNAC. The specificity of CNB (range, 86%-100%) also is generally higher than that of FNAC (range, 48%-100%).[5, 6, 14-16] Although the success rates of CNB reportedly are higher, this technique also has some disadvantages compared with FNAC: ie, it is a more time-consuming, more invasive procedure, and a definitive diagnosis takes 1 day to several days. However, the benefits of CNB over FNAC—ie, higher sensitivity, the ability to distinguish between in situ and invasive carcinoma, and the ability to assess receptor status—favors its use as the preferred diagnostic tool in at least certain subsets of patients. Because of these benefits of CNB, there is a trend away from FNAC as a first-line diagnostic method for breast lesions to an increased use of CNB and VAB in many institutions.
The literature is limited regarding the use of breast FNAC in BRCA mutation carriers, but it seems reasonable to hypothesize a limited sensitivity of FNAC, since these lesions often are detected by screening and, thus, are small and nonpalpable. In addition to having an increased breast cancer risk, screened BRCA1/BRCA2 mutations carriers are relatively young, so they have a higher incidence of both breast cancer precursor lesions and benign lesions (eg fibroadenomas and proliferative fibrocystic changes), which are associated with diagnostic difficulty using FNAC.[17, 18] Moreover, these usually young patients may develop poorly differentiated, fast-growing carcinomas, underlining the importance of a sensitive pathologic diagnostic tool that produces minimal false-negative results to prevent treatment delay.[13, 19] The number of inconclusive results and the false-positive rate also have to be minimal, because these obviously lead to anxiety and overtreatment, respectively, especially in patients who choose to undergo (bilateral) breast ablation for treatment and risk-reduction purposes.
The objectives of the current study were to evaluate the accuracy of FNAC in BRCA mutation carriers and to generate recommendations regarding the most optimal diagnostic method. Because MRI is used increasingly as a screening method for breast cancer, including non-BRCA mutation carriers, the results of this study may provide important information regarding the diagnostic value of FNAC in other screen-detected lesions for other subsets of high-risk patients.
MATERIALS AND METHODS
All BRCA1/BRCA2 mutation carriers who underwent FNAC from 1998 to December 2011 were selected from the BRCA1/BRCA2 mutation carriers registered in the database of the Rotterdam Family Cancer Clinic who visited the Erasmus Medical Center, Daniel den Hoed Cancer Center (Rotterdam, the Netherlands). These women came either because of symptoms or for screening. From 1998 up to 2007, breast cancer surveillance for BRCA1/BRCA2 mutation carriers consisted of biannual clinical breast examination and annual imaging, including mammography and MRI (performed within a 6-week period). From 2007, regular surveillance consisted of biannual clinical breast examination and yearly imaging examination, including both mammography and MRI, alternating every 6 months, according to institutional and national guidelines. FNAC was followed by surveillance, CNB, VAB, or surgical excision.
Age at diagnosis and palpability of the lesion were recorded.
Mammography has been performed at our institution using a digital mammographic unit since 2005. In the patients studied, standard craniocaudal and oblique views were obtained with additional magnification views if necessary. Radiologic data recorded included the results from mammogram, MRI, and, if applicable, ultrasound. An ultrasound was indicated if patients had palpable lesions and/or lesions classified according to the American College of Radiologists' Breast Imaging-Reporting and Data System (BIRADS) as BIRADS 0 (indefinite), BIRADS 3 (probably benign), BIRADS 4 (suspicious for malignancy), or BIRADS 5 (malignant) on mammography or MRI. According to this system BIRADS 1 indicates normal, BIRADS 2 indicates a benign lesion, and BIRADS 6 indicates histologically proven malignancy.
Indications for FNAC included clinical palpable lesions or BIRADS 3, BIRADS 4, or BIRADS 5 lesions on ultrasound. If a lesion was visible on ultrasound, then FNAC was performed by the radiologist using a 21-gauge or 22-gauge needle. Two to 4 passes were performed to ensure proper sampling. The needle placement during ultrasound-guided FNAC was recorded by still pictures. In palpable lesions that were not visible on ultrasound, FNAC often was performed by the clinician. There was no immediate evaluation for adequacy. Histology specimens were obtained with a 14-gauge spring-loaded gun needle (CNB) or with a vacuum-assisted 10-gauge biopsy probe and always under ultrasound guidance.
Pathologic Features and Calculation of the Accuracy of Fine-Needle Aspiration Cytology Parameters
The results of the FNAC were divided into 5 categories (cytology codes), including C1 (inadequate material), C2 (benign), C3 (atypia, probably benign), C4 (suspect for malignancy), and C5 (malignant). The cutoff point for satisfying cellularity was 6 epithelial groups; however, for clinical features of a cyst, C2 was used in the presence of macrophages and cystic fluid, even if there were <6 groups of epithelial cells. FNAC accuracy parameters were calculated by taking the outcome of the histologic diagnosis (by either CNB, VAB, or surgical excision) or surveillance as the reference standard. Benign histology comprised fibrocystic changes, fibroadenomas, and lipomas. Malignant histology included (in situ) carcinoma. Histological diagnosis had to be performed within 4 months after the FNAC. Patients who underwent histological examination >4 months after FNAC were included in the clinical follow-up analysis.
The result of each FNAC followed by a histologic diagnosis was defined as true-positive, false-positive, true-negative, or false-negative. Categories C4 and C5 were defined as malignant, and C2 was defined as benign. The C1 group was excluded from analysis along with C3 group, because these categories included lesions of an uncertain nature, requiring further investigation. A true-positive FNAC was defined as C4 or C5 result followed by a malignant diagnosis on histology (either in situ or invasive carcinoma). A true-negative FNAC was defined as a C2 result followed by a benign, definitive diagnosis after histologic examination or clinical/radiologic follow-up.
Calculated FNAC parameters included sensitivity (true-positives/[true-positives + false-negatives]), specificity (true-negatives/[true-negatives + false-positives]), positive predictive value (true-positives/total number of positive FNACs), and negative predictive value (true-negatives/all negative FNACs). The false-positive rate was calculated as false-positives/(false-positives + true-negatives), and the false-negative rate was calculated as false-negatives/false-negatives + true-positives. Finally, accuracy was calculated as the sum of all true-positive and true-negative FNACs divided by the total number of all positive and negative FNACs (including C2, C4, and C5).
Of 792 BRCA1/BRCA2 mutation carriers who visited the clinic after 1998 (age range, 20-68 years), 222 patients underwent FNAC of the breast, which resulted in a total of 320 FNACs (some patients underwent more than 1 FNAC). Data regarding palpability were recorded for 314 lesions. The majority of these lesions (58.3%) were nonpalpable.
Ultrasound was performed as a consequence of 253 lesions visible on mammography and/or MRI: Ultrasound was categorized as BIRADS 0 in 3 lesions (1.2%), BIRADS 1 in 27 lesions (10.7%), BIRADS 2 in 53 lesions (20.9%), BIRADS 3 in 93 lesions (36.7%), BIRADS 4 in 72 lesions (28.4%), and BIRADS 5 in 5 lesions (2%).
Size on ultrasound was mentioned in the radiology report for 106 lesions. The majority of these lesions (66 of 106; 62.3%) were smaller or were equal to 1 cm.
Of all 320 FNACs, 82 samples (25.6%) were diagnosed as C1, 142 (44.3%) were diagnosed as C2, 7 were diagnosed (2.2%) as C3, 17 were diagnosed (5.3%) as C4, and 72 (22.5%) were diagnosed as C5. In 150 patients, the FNAC was followed by histology examination within 4 months. This included CNB/VAB (63 patients), wide local excision (44 patients), prophylactic mastectomies (14 patients), and therapeutic mastectomies (45 patients). In 4 patients, more than 1 histologic method was used to reach the final diagnosis. The definitive histologic diagnosis was benign in 41 patients and malignant in 109 patients. Table 1 provides an overview of the FNAC results and the corresponding histologic diagnoses. The remaining 150 patients with benign or inconclusive FNAC results were followed clinically and radiologically. In total, 20 patients with benign FNAC results were lost to follow-up. The histologic examination in the 84 true-positive FNACs (C4 or C5 followed by malignant histology) included 81 invasive ductal carcinomas, 1 medullary carcinoma, 1 ductal carcinoma in situ, and 1 lobular carcinoma in situ.
Table 1. Results of Fine-Needle Aspiration Cytology Followed by Histology
Fine-Needle Aspiration Cytology Accuracy Parameters
The calculation of FNAC accuracy parameters including, patients with either histologic or clinical follow-up, revealed the following results: the false-negative rate was 7.7%, the false-positive rate was 3.7%, sensitivity was 92.3%, specificity was 96.3%, and accuracy was 94.7% The positive predictive value was 94.4%, and the negative predictive value was 94.9%.
Calculation of FNAC accuracy parameters, including only those patients who had histology examinations within 4 months after FNAC, revealed the following results: sensitivity was 92.3%, specificity was 81.5%, the positive predictive value was 94.4%, the negative predictive value was 75.9%, the false-negative rate was 7.7%, the false-positive rate was 18.5%, and accuracy was 89.8%.
In case of clinical or radiologic suspicion or uncertainty after an inconclusive or benign FNAC result, histology was obtained. From the total number of FNACs, 82 were inconclusive and had a cytology code of C1. The size of these lesions varied between 5 mm and 10 mm. Histology was performed in 27 C1-coded lesions, of which 15 lesions turned out to be malignant (ductal carcinoma). Of the remaining 55 patients who had lesions coded as C1, 12 underwent a second FNAC. In 10 patients, the second FNAC was benign (C2); and, in 2 patients, again, it was inconclusive (C1). In 2 patients who were diagnosed with C1 lesions, a malignancy was diagnosed during regular follow-up (after 6 months and 10 months, respectively). The remaining lesions were followed clinically and radiologically because of very low suspicion, and no malignancy was revealed.
A substantial proportion of patients (35%) with malignant FNAC results underwent CNB/VAB upfront surgical resection to confirm the diagnosis. In the entire series of patients who had benign FNAC results without histologic follow-up (113 patients), no malignancies were detected during long-term clinical and radiologic surveillance (median follow-up, 84 months).
Features Influencing Fine-Needle Aspiration Cytology Accuracy
There was no association between BIRADS category and the FNAC success rate. The FNAC success rate increased in lesions >1 cm compared with smaller lesions, which also held true for palpability (Table 2). Of the 82 lesions with unsatisfactory composition (C1), the majority were small and nonpalpable (50 lesions).
Table 2. Comparison of the Fine-Needle Aspiration Cytology Success Rates According to Size and Palpability of the Breast Lesion
Of 142 patients who had benign FNAC results (C2), 7 were diagnosed with malignancy after histology. In all 7 of these patients, the final diagnosis on histology was grade 3 invasive ductal carcinoma. The indication for histologic examination after a benign FNAC result included a discrepancy between radiologic findings (either ultrasound, mammogram, and/or MRI) and pathologic findings. The greatest tumor dimensions ranged from 4 mm to 16 mm. On mammography, 4 of these false-negative cases were categorized as BIRADS 2, 2 were categorized as BIRADS 4, and 1 was categorized as BIRADS 1. Of 5 of those lesions, MRI categorized 2 lesions as BIRADS 3, 2 lesions as BIRADS 4, and 1 lesion as BIRADS 0. Ultrasound categorized 2 lesions as BIRADS 2 and 5 lesions as BIRADS 4.
Histologic examination in the 5 false-positive FNACs revealed proliferative lesions in all patients, including 1 tubular adenoma, 1 papilloma, 2 cases of atypical ductal hyperplasia, and 1 case of sclerosing adenosis. All of these lesions were nonpalpable and measured <1 cm. Mammography categorized 2 of these lesions as BIRADS 0, 2 lesions as BIRADS 2, and 1 lesion as BIRADS 4. MRI categorized 3 lesions as BIRADS 4 and 2 lesions as BIRADS 0. Ultrasound categorized 1 lesions as BIRADS 1, 1 lesion as BIRADS 2, and 3 lesions as BIRADS 4.
The definite histologic diagnosis was confirmed by a CNB in 1 patient, by wide local excision in 3 patients, and by mastectomy (including sentinel lymph node procedure) in 1 patient. This patient underwent mastectomy based on the preference of the patient 2 years after she underwent contralateral mastectomy for breast carcinoma.
There is increasing literature regarding the advantages and disadvantages of FNAC in diagnosing breast lesions, but the results of those studies may not hold completely true for the often screen-detected lesions of high-risk patients, including BRCA1/BRCA2 mutation carriers. Therefore, we set up this study to analyze the suitability of FNAC in these high-risk patients. Because of the annual screening program of BRCA1/BRCA2 mutation carriers in the Netherlands, breast lesions are mostly identified at an early stage and, thus, are small in size. Although our study was restricted to this subgroup of high-risk patients, the results are unlikely to be specific for BRCA1/BRCA2 mutation carriers and probably reflect the performance of FNAC in intensively screened, high-risk patients in general.
Our study demonstrated decreased FNAC success rates in small and nonpalpable lesions, which is in line with previous studies.[5, 9, 10] The FNAC accuracy parameters were comparable to the best results reported in the literature, considering the general population. However, these reported success rates usually do not include inconclusive cases and do not consider the number of patients undergoing both FNAC and a confirmatory CNB/VAB upfront surgery. Decreased FNAC accuracy in low-grade carcinomas and lobular carcinomas has been reported. However, this could not explain the false-negative results in our study, because all of these patients were diagnosed with high-grade ductal carcinoma after histologic examination. All of our 5 false-positive FNACs cases had proliferative lesions, which is consistent with reports in the literature of diagnostic difficulty with papillary and hyperplasic lesions based on FNAC.[9, 12] However, the surgical consequences of a malignant FNAC may be relatively large in this subset of patients compared with the general population. Although these patients have no contraindication for breast-sparing surgery in case of malignancy, the threshold for mastectomy is lower because of their high life-time risk. Thus, the impact of a false-positive FNAC result may be huge in these generally young patients, increasing the need for a definite preoperative diagnosis, preferably by using a single procedure.
To our knowledge, this is the first study reporting on the accuracy of FNAC in a large series of BRCA1/BRCA2 mutation carriers. However, we could not directly compare the accuracy of FNAC and CNB/VAB in our patients, because they initially underwent either 1 or the other procedure. Only half of these patients undergoing FNAC underwent a subsequent histologic procedure. However, most of the remaining patients had a clinical/radiological follow-up for several years.
The diagnostic performance of FNAC for benign lesions (C2) reached high accuracy in our series. No malignancies were detected during long-term clinical and radiologic surveillance for the lesions that were diagnosed as benign on FNAC without histologic confirmation, supporting the use of FNAC in this subset of patients. In cases of a discrepancy between the FNAC results and clinical/radiologic findings, patients must undergo histologic biopsy, as verified by our false-negative rate. Although this is a straightforward conclusion, it may be hard to apply in daily practice, because the role of clinical examination of these early detected lesions is limited, and the radiologic findings are often indefinite. This underlines the necessity of discussing these patients in a multidisciplinary meeting.
The rate of inconclusive FNAC (C1) was 25.6% in this study, which is relatively high, resulting in increased patient anxiety and costs for a second procedure. In addition, the amount of false-positive results, although an absolute low number, is worrisome. A substantial proportion of patients (35%) with a malignant FNAC result underwent a CNB upfront the surgical resection to confirm the diagnosis, which also results in prolonged anxiety, treatment delay, and increased costs.
There are several potential reasons for our inadequate and false-positive rates. Our institute uses a limit of 15% of nondiagnostic samples and 1% for false-positive cases, and these rates are evaluated yearly but not on an individual, per radiologist or cytopathologist basis. The number of inadequate and false-positive cases may have been influenced by the level of experience of the aspirator or cytopathologist, which is known from previous studies. However, our data are a realistic reflection of daily practice over the last decade. Therefore, no internal review was performed for the insufficient and false-positive cases, because this was not the aim of the study. The performance of FNAC, however, could be improved by applying criteria of minimum levels of training for aspirators and cytopathologists.
In addition to these sampling and interpretation issues, the relatively high rate of inadequate and false-positive cases probably is affected by the size and type of lesions in this patient subset, because our FNAC performance has been better in the general population during recent years (inadequacy rate, <15%; false-positive rate, <1%).
In conclusion, based on the high accuracy rates in radiologic and pathologic benign lesions, FNAC may be considered for radiologic (probably) benign lesions, although its use may be limited by a high overall rate of insufficient material, requiring additional tests. The success rate of FNAC in suspicious lesions, especially when they are small and nonpalpable, conversely, has substantial limitations, including both a high false-positive rate and a large proportion of patients requiring more than 1 diagnostic procedure (FNAC and confirmatory CNB/VAB) upfront surgery, which favors a histological biopsy as the preferred primary diagnostic tool.
No specific funding was disclosed.
CONFLICT OF INTEREST DISCLOSURES
The authors made no disclosures.