Comparison of PAX8 Expression in Breast Carcinoma Using MRQ50 and BC12 Monoclonal Antibodies

Immunohistochemical Characterization of a Large Cohort of Triple Negative Breast Cancer

Introduction. Triple negative breast carcinomas are characterized by a lack of hormone receptor and HER2 expression and inconsistent expression of breast-specific immunohistochemical markers. The expression of many site-specific markers in these tumors is largely unknown. The objective of the study was to examine the expression of widely used immunohistochemical markers on a large cohort of triple negative breast cancer. Methods. Sections from tissue microarrays were stained with 47 markers using routine protocols. Most markers were scored using a modified Allred method. ATRX, BAP1, SMAD4, e-cadherin, and beta-catenin were scored as retained or lost. Mammaglobin was considered positive if there was at least moderate intensity staining in any tumor cells. P16 was scored as overexpressed or not overexpressed; p53 was scored as wildtype, overexpressed, null, or cytoplasmic. Results. The cohort consisted of 639 tumors including 601 primary and 32 metastases. Overall, 96% expressed GATA3, mammaglobin, and/or SOX10 while 97% of no special type tumors expressed this panel. Carcinoma of apocrine differentiation demonstrated an AR positive, SOX10 negative, K5 negative/focal immunophenotype. PAX8 (SP348), WT1, Napsin A, and TTF1 (8G7G3/1) were never or rarely expressed while CA9, CDX2, NKX3.1, SATB2 (SATBA410), synaptophysin, and vimentin were variably expressed. Conclusions. Almost all TNBC express at least 1 of the 3 IHC markers: GATA3, mammaglobin, and/or SOX10. Carcinoma of apocrine differentiation is characterized by an AR positive, SOX10 negative, K5 negative or focal immunophenotype. Cautious interpretation of so-called site-specific markers, with knowledge of antibody clones, is required in excluding the diagnosis of triple negative breast cancer.

SOX17: A Highly Sensitive and Specific Immunomarker for Ovarian and Endometrial Carcinomas

PAX8 is the most commonly used immunomarker to link a carcinoma to the gynecologic tract; however, it lacks specificity. Through mining The Cancer Genome Atlas mRNA expression profile data, we identified SOX17 as a potential specific marker at the mRNA level for gynecologic tumors. To evaluate the utility of this marker in the identification of the gynecologic origin of a given carcinoma, we performed immunochemical staining in a large cohort of ovarian and endometrial cancer cases (n = 416), together with a large cohort of solid tumors from other organs (n = 1544) in tissue microarrays. Similar to PAX8, SOX17 was highly expressed in different subtypes of ovarian carcinoma (97.5% for SOX17 vs 97% for PAX8 in serous carcinoma, 90% vs 90% in endometrioid carcinoma, and 100% vs 100% in clear cell carcinoma), except for mucinous carcinoma (0% vs 27%), and was also highly expressed in different subtypes of endometrial carcinoma (88% vs 84% in endometrioid carcinoma, 100% vs 100% in serous and clear cell carcinoma). SOX17 was not expressed in thyroid and renal cell carcinomas, whereas PAX8 expression was high (86% and 85%, respectively). In addition, SOX17 was expressed at low levels in cervical adenocarcinoma (20%) and had no expression in cervical squamous carcinoma, mesothelioma, and carcinomas from the breast, lung, pancreas, colon, stomach, liver, bladder, and salivary gland. Our data indicate that SOX17 is not only a sensitive but also a specific marker for the origin of ovarian and endometrial carcinomas.

Identifying SOX17 as a Sensitive and Specific Marker for Ovarian and Endometrial Carcinomas

Similar to PAX8, SOX17 was recently identified as a master transcription factor of ovarian cancer based on RNA sequencing data. We explored SOX17 utility in diagnosing ovarian tumors and other gynecologic tumors. We systematically evaluated SOX17 expression on tissue microarrays of 398 ovarian tumors of various types, 93 endometrial carcinomas, 80 cervical carcinomas, and 1371 nongynecologic carcinomas, such as those of kidney, thyroid, breast, colon, bladder, liver, bile duct, adrenal gland, pancreas, brain, and lung and malignant melanoma. In addition, we evaluated SOX17 expression in whole tissue sections from 60 gynecologic carcinomas and 10 angiosarcomas. The results demonstrated that SOX17 was highly expressed in most ovarian and endometrial tumors with strong intensity. However, unlike PAX8, it was predominately negative in other tested tumor types, including kidney and thyroid tumors. In particular, SOX17 was highly expressed in the following pathologic subtypes of ovarian tumors: serous carcinoma, clear cell carcinoma, endometrioid carcinoma, and germ cell tumors. SOX17 was mostly negative in mucinous carcinoma and sex cord stromal tumors. In addition, SOX17 was expressed in vascular endothelial cells and was positive in all tested angiosarcomas. In summary, our results demonstrate that SOX17 is a sensitive and specific marker for ovarian nonmucinous carcinomas and endometrial carcinomas. For ovarian germ cell tumors and angiosarcomas, SOX17 demonstrates higher specificity than PAX8, with comparable sensitivity. Furthermore, SOX17 positivity in endothelial cells serves as an internal positive control, making it an excellent marker.

New Challenges in the Differential Diagnosis of High-Grade Triple-Negative Breast Cancer and Serous Carcinoma

While screening has improved early detection of primary breast cancers, it may also identify metastasis to the breast in rare instances. High-grade carcinomas identified on breast screening may have non-specific morphology and immunoprofiles, making distinction from metastasis problematic. High-grade carcinomas frequently lose expression of specific tumor markers. New evidence specifically challenges GATA3/PAX8 exclusivity in the differential diagnosis of high-grade triple-negative breast cancer and high-grade serous carcinoma of müllerian origin. This case series provides a careful and detailed review of immunohistochemistry interpretation, with focus on PAX8, and the potential pitfalls in making a definitive pathological diagnosis, which is essential in determining oncological treatment options.

Lobular Carcinoma of the Breast Metastatic to the Ovary: A Clinicopathologic Study of 38 Cases

We evaluated the clinicopathologic features of 38 cases of metastatic lobular (n=33) or predominantly lobular (n=5) carcinoma involving the ovary. The patients were from 39 to 91 years of age (mean: 53 y). In 2 cases, the breast primary and ovarian metastasis were diagnosed synchronously, and in 5, the breast primary was only discovered after the metastatic carcinoma in the ovary was found. In the majority of cases (79%), both ovaries were involved; the mean ovarian tumor size was 5.9 cm. The ovarian tumors demonstrated a range of architectural patterns including macronodular (71%), diffuse/solid growth (87%), single-cell infiltration (87%), cords (74%), and small nests/clusters (50%). Nine cases demonstrated focal signet ring cell morphology. The associated stromal reaction ranged from none to marked, with almost half of cases demonstrating a marked stromal response, largely prominent sclerosis. A variety of neoplasms, most typically sex cord-stromal tumors, lymphoma/leukemia, and desmoplastic small round cell tumor, may enter the differential. In addition to the obvious help afforded in most cases by the clinical history, a combination of judicious sampling, particularly to unearth the delicate cords or single-cell growth of lobular carcinoma, appropriate consideration of the cytologic features of the neoplastic cells, and immunohistochemistry can resolve the diverse issues in differential diagnosis that may arise.

PAX-8 Expression in Salivary Duct Carcinoma

Salivary duct carcinoma (SDC) is a high-grade adenocarcinoma resembling breast ductal carcinoma. It accounts for ~10% of malignant tumors of the salivary glands. Most cases show expression of CK7 and androgen receptor. PAX-8 is a transcription factor, with expression reported in renal, Müllerian, and thyroid carcinomas. Previous studies have described an absence of PAX-8 immunostaining in most primary salivary gland neoplasms, including SDCs. However, PAX-8 expression is frequently found in neoplasms that can metastasize to salivary glands, suggesting the possibility that this protein can be used to differentiate SDC from secondary neoplastic involvement of the salivary gland. We evaluated the expression of PAX-8 in 14 cases of SDC from our institution. One case showed diffuse moderate to strong PAX-8 positivity, while 2 tumors showed focal weak staining. Therefore, we conclude that although the majority of SDC are negative for PAX-8, rare diffuse positivity can be seen in these primary salivary gland tumors. This could potentially pose difficulty in ruling out metastatic disease from another PAX-8-positive primary neoplasm.

Polyclonal PAX8 expression in carcinomas of the biliary tract - Frequent non-specific staining represents a potential diagnostic pitfall

Paired box protein 8 (PAX8) is a transcription factor that is considered a relatively specific marker of carcinomas of the thyroid, kidney, and Müllerian/Wolffian duct derivatives. Unexpected PAX8 immunoreactivity has occasionally been reported in other tumors. The frequency of PAX8 expression in carcinomas of the biliary tract is not well studied. We evaluated the immunohistochemical expression of PAX8 in 73 cases of biliary tract carcinoma. We found that 28 of 73 (38%) biliary tract carcinomas had variable immunoreactivity for PAX8, assessed by a widely used polyclonal antibody (ProteinTech Group, Chicago, IL). This included 3 (4%) of cases with strong diffuse, and 14 (19%) of cases with strong focal staining. Strong PAX8 expression was more frequent in distal bile duct carcinomas than other biliary sites (p = 0.015), and showed a weak association with advanced T stage (T3-T4 versus T1-T2; p = 0.09). No correlation was observed between PAX8 positivity and age at diagnosis, gender, or lymph node metastasis. The 28 polyclonal PAX8-positive cases were largely negative for monoclonal PAX8 and PAX6 immunostains, with only rare tumor cells with weak immunoreactivity being present in a subset of cases. We show that a substantial fraction of biliary tract carcinomas exhibit immunoreactivity with a widely used polyclonal PAX8 antibody. Pathologists should be aware of this potential pitfall during the diagnostic workup of hepatobiliary lesions to avoid misdiagnosis as a metastasis from a PAX8-positive tumor.

PAX8 Expression in Breast Cancer

PAX8 expression is frequently detected in renal, thyroidal, and Müllerian carcinomas, and PAX8 immunohistochemistry is often used to confirm the origin of these tumors. Tumors metastatic to the breast may masquerade as primary breast lesions. PAX8 is strongly expressed in tumors of Müllerian origin and largely negative in breast primaries, but an immunohistochemical expression of PAX8 in breast cancer has not been systematically evaluated in a large series. We analyzed 266 cases of invasive carcinoma of the breast on tissue microarrays and whole tissue sections with a PAX8 monoclonal antibody. Both the extent (focal or diffuse) and intensity (weak, moderate, or strong) of nuclear staining were assessed in the tumor cells. In total, 16 cases (6.02%) were positive for PAX8 (12 with weak and 4 with moderate staining). Expression was diffuse in 7 cases and focal in 9 cases. All 16 PAX8-positive tumors were histologic grade III invasive ductal carcinomas, 13 of these were triple-negative, 2 were HER2-positive, only and 1 was progesterone receptor-positive only. Strong PAX8 nuclear expression was not seen in any of the cases. PAX8 was negative in breast tumors with neuroendocrine features. Our study demonstrated a low rate of PAX8 expression in breast cancer. When present, PAX8 expression was only seen in high-grade invasive ductal carcinomas, mostly triple-negative. The presence of PAX8 immunoreactivity alone cannot exclude mammary origin, especially when only weak to moderate staining is observed, so the correlation with available clinical and pathologic data helps to ensure an accurate diagnosis.

Assessment of stromal tumor infiltrating lymphocytes and immunohistochemical features in invasive micropapillary breast carcinoma with long-term outcomes

PURPOSE

We studied the long-term outcomes of invasive micropapillary carcinoma (IMPCs) of the breast in relation to stromal tumor infiltrating lymphocytes (sTILs), prognostic biomarkers and clinicopathological features.

METHODS

Stage I-III IMPCs treated with upfront surgery at our institution (January 2000 and December 2016) were included. Central pathology review was performed and sTILs (including zonal distribution and hot spot analysis) and tumor-associated plasma cells (TAPC) were evaluated. Expression of P53, BCL2, FOXP3, and WT1, which are variably linked to breast cancer prognosis, was measured by immunohistochemistry using tissue microarrays. Time-to-event endpoints were distant recurrence free interval (DRFI) and breast cancer-specific survival (BCSS).

RESULTS

We included 111 patients of whom 59% were pure IMPCs. Standard clinicopathological features were comparable between pure and non-pure IMPCs. Overall, the mean sTILs level was 20% with higher proportion of sTILs present at the invasive front. There were no significant differences between pure- and non-pure IMPCs in sTILs levels, nor in the spatial distribution of the hot spot regions or in the distribution of TAPC. Higher sTILs correlated with worse DRFI (HR = 1.55; p = 0.0172) and BCSS (HR = 2.10; p < 0.001).

CONCLUSIONS

Clinicopathological features, geographical distribution of sTILs and TAPC are similar between pure and non-pure IMPCs. Despite a high proportion of grade 3 tumors and lymph node involvement, we observed a low rate of distant recurrences and breast cancer-related death in this cohort of stage I-III IMPCs treated with primary surgery. Caution in interpretation of the observed prognostic correlations is required given the very low number of events, warranting validation in other cohorts.

Do You Know the Details of Your PAX8 Antibody? Monoclonal PAX8 (MRQ-50) Is Not Expressed in a Series of 45 Medullary Thyroid Carcinomas

Medullary thyroid carcinomas display cytologic and architectural features that can simulate various primary and metastatic neoplasms. PAX8 immunoexpression in neuroendocrine neoplasms yielded antibody-dependent findings. Since the data regarding the expression profile of monoclonal PAX8 (MRQ-50) antibody is limited in large series of medullary thyroid carcinomas, this study investigated the expression profile of PAX8 (MRQ-50) in a series of 45 medullary thyroid carcinomas. PAX8 (MRQ-50) expression was noted in the thyroid follicular epithelial cells surrounding the tumor and was negative in all medullary thyroid carcinomas. In addition, twenty medullary thyroid carcinomas showed scattered entrapped thyroid follicular epithelial cells at the periphery of the tumor. Entrapped follicular epithelial cells were positive for PAX8 and thyroglobulin, and were negative for monoclonal CEA and calcitonin. A panel approach combining monoclonal antibodies to transcription factors, hormones and cell-specific peptides often assist diagnosticians in the workup of the cellular origin of a neuroendocrine neoplasm. Since PAX8 immunostaining is dependent on the antibody characteristics in neuroendocrine neoplasms, pathologists should be aware of the details of the PAX8 antibody used in a particular case.