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Context.—: Plasmacytoid urothelial carcinoma (PC-UC) is an aggressive variant of urothelial carcinoma (UC), characterized by loss of E-cadherin (E-Cad)-mediated intercellular adhesion. Loss of E-Cad by immunohistochemistry can help diagnose PC-UC; however, sensitivity is limited. Expression of other cadherin-catenin adhesion complex members, that is, p-120 catenin (p-120) and β-catenin (B-Cat), which are diagnostically useful for lobular breast carcinoma, remains unknown in UC., Objective.—: To determine the utility of p-120 and B-Cat in conventional and variant UC., Design.—: E-cadherin, B-Cat, and p-120 immunohistochemistry was performed in 25 conventional UCs and 33 variant UCs, including 22 PC-UCs, 6 sarcomatoid UCs (SUCs), and 5 micropapillary UCs. Membranous staining for all biomarkers was considered normal; however, any cytoplasmic staining or an absence of staining was considered diagnostically abnormal. Next-generation sequencing was performed on 8 PC-UC cases., Results.—: E-cadherin, B-Cat, and p-120 showed membranous staining in all conventional and micropapillary UCs. In contrast, most PC-UCs were negative for E-Cad (17 of 22; 77%) with an additional 2 of 22 cases (9%) showing cytoplasmic with partial membranous staining. p-120 catenin demonstrated cytoplasmic or negative staining in 21 of 22 cases (95%). Most SUCs showed an absence of E-Cad (5 of 6; 83%) and cytoplasmic or negative p-120 in 5 of 6 cases (83%). Staining for B-Cat was also abnormal in a subset of PC-UCs and SUCs. Five PC-UC cases that harbored CDH1 gene variants were p-120 cytoplasmic positive., Conclusions.—: p-120 catenin is a useful adjunct biomarker to E-Cad in the clinically important distinction of PC-UC and SUC from conventional UC. In particular, the combination of cytoplasmic p-120 and loss of E-Cad is strongly supportive of PC-UC and SUC., Competing Interests: The authors have no relevant financial interest in the products or companies described in this article.

Transcription factor E3-rearranged renal cell carcinoma (TFE3-RCC) has heterogenous morphologic and immunohistochemical (IHC) features.131 pathologists with genitourinary expertise were invited in an online survey containing 23 questions assessing their experience on TFE3-RCC diagnostic work-up.Fifty (38%) participants completed the survey. 46 of 50 participants reported multiple patterns, most commonly papillary pattern (almost always 9/46, 19.5%; frequently 29/46, 63%). Large epithelioid cells with abundant cytoplasm were the most encountered cytologic feature, with either clear (almost always 10/50, 20%; frequently 34/50, 68%) or eosinophilic (almost always 4/49, 8%; frequently 28/49, 57%) cytology. Strong (3+) or diffuse (>75% of tumour cells) nuclear TFE3 IHC expression was considered diagnostic by 13/46 (28%) and 12/47 (26%) participants, respectively. Main TFE3 IHC issues were the low specificity (16/42, 38%), unreliable staining performance (15/42, 36%) and background staining (12/42, 29%). Most preferred IHC assays other than TFE3, cathepsin K and pancytokeratin were melan A (44/50, 88%), HMB45 (43/50, 86%), carbonic anhydrase IX (41/50, 82%) and CK7 (32/50, 64%). Cut-off for positive TFE3 fluorescent in situ hybridisation (FISH) was preferably 10% (9/50, 18%), although significant variation in cut-off values was present. 23/48 (48%) participants required TFE3 FISH testing to confirm TFE3-RCC regardless of the histomorphologic and IHC assessment. 28/50 (56%) participants would request additional molecular studies other than FISH assay in selected cases, whereas 3/50 participants use additional molecular cases in all cases when TFE3-RCC is in the differential.Optimal diagnostic approach on TFE3-RCC is impacted by IHC and/or FISH assay preferences as well as their conflicting interpretation methods., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2021. No commercial re-use. See rights and permissions. Published by BMJ.)

Morphologic (ie, hematoxylin and eosin) evaluation of the Mullerian tract remains the gold standard for diagnostic evaluation; nevertheless, ancillary/biomarker studies are increasingly utilized in daily practice to assist in the subclassification of gynecologic lesions and tumors. The most frequently utilized "biomarker" technique is immunohistochemistry; however, in situ hybridization (chromogenic and fluorescence), chromosomal evaluation, and molecular analysis can also be utilized to aid in diagnosis. This review focuses on the use of immunohistochemistry in the Mullerian tract, and discusses common antibody panels, sensitivity and specificity of specific antibodies, and points out potential diagnostic pitfalls when using such antibodies.

Intraductal carcinoma of the prostate (IDC-P) has been recently recognized by the World Health Organization classification of prostatic tumors as a distinct entity, most often occurring concurrently with invasive prostatic adenocarcinoma (PCa). Whether documented admixed with PCa or in its rare pure form, numerous studies associate this entity with clinical aggressiveness. Despite increasing clinical experience and requirement of IDC-P documentation in protocols for synoptic reporting, the specifics of its potential contribution to assessment of grade group (GG) and cancer quantitation of PCa in both needle biopsies (NBx) and radical prostatectomy (RP) specimens remain unclear. Moreover, there are no standard guidelines for incorporating basal cell marker immunohistochemistry (IHC) in the diagnosis of IDC-P, either alone or as part of a cocktail with AMACR/racemase. An online survey containing 26 questions regarding diagnosis, reporting practices, and IHC resource utilization, focusing on IDC-P, was undertaken by 42 genitourinary subspecialists from 9 countries. The degree of agreement or disagreement regarding approaches to individual questions was classified as significant majority (>75%), majority (51% to 75%), minority (26% to 50%) and significant minority (≤25%). IDC-P with or without invasive cancer is considered a contraindication for active surveillance by the significant majority (95%) of respondents, although a majority (66%) also agreed that the clinical significance/behavior of IDC-P on NBx or RP with PCa required further study. The majority do not upgrade PCa based on comedonecrosis seen only in the intraductal component in NBx (62%) or RP (69%) specimens. Similarly, recognizable IDC-P with GG1 PCa was not a factor in upgrading in NBx (78%) or RP (71%) specimens. The majority (60%) of respondents include readily recognizable IDC-P in assessment of linear extent of PCa at NBx. A significant majority (78%) would use IHC to confirm or exclude intraductal carcinoma if other biopsies showed no PCa, while 60% would use it to confirm IDC-P with invasive PCa in NBx if it would change the overall GG assignment. Nearly half (48%, a minority) would use IHC to confirm IDC-P for accurate Gleason pattern 4 quantitation. A majority (57%) report the percentage of IDC-P when present, in RP specimens. When obvious Gleason pattern 4 or 5 PCa is present in RP or NBx, IHC is rarely to almost never used to confirm the presence of IDC-P by the significant majority (88% and 90%, respectively). Most genitourinary pathologists consider IDC-P to be an adverse prognostic feature independent of the PCa grade, although recommendations for standardization are needed to guide reporting of IDC-P vis a vis tumor quantitation and final GG assessment. The use of IHC varies widely and is performed for a multitude of indications, although it is used most frequently in scenarios where confirmation of IDC-P would impact the GG assigned. Further study and best practices recommendations are needed to provide guidance with regards to the most appropriate indications for IHC use in scenarios regarding IDC-P.

Perivascular epithelioid cell tumor (PEComa) belongs to a family of tumors characterized by coexpression of melanocytic and muscle markers. Recent studies have shown that sporadic and tuberous sclerosis complex-associated PEComa may respond to mTOR inhibitors underscoring the importance of recognizing this tumor. However, its occurrence in the gynecologic tract continues to be disputed owing to its common misclassification as other types of uterine sarcoma and its controversial relationship with epithelioid smooth muscle tumors. To more fully characterize PEComa of the female genital tract, 16 cases of gynecologic PEComa were identified (1990 to 2012) and formed the basis of this study. Each case was analyzed for conventional morphologic and immunohistochemical characteristics established for PEComa of extrauterine sites; clinical outcome data were obtained for all cases. The 16 patients were aged 28 to 60 (mean 49; median 50) years, and 1 had a history of tuberous sclerosis complex. Thirteen cases were primary of the uterus, 2 of the adnexa, and 1 of the vagina. Tumor size ranged from 0.3 to 25.0 (mean 8.7) cm. Three patients died of disease, 6 were alive with disease, and 7 were alive without evidence of disease at last follow-up (1 mo to 13 y follow-up; mean 26 mo). All patients with an adverse outcome met established criteria for malignancy as proposed for extrauterine sites (ie, 2 or more features present: size ≥5 cm, high-grade nuclear features, infiltration, necrosis, lymphovascular invasion, or a mitotic rate ≥1/50 high-power fields). Of the melanocytic markers, HMB45 was most commonly expressed (16/16 positive, 100%), followed by microphthalmia transcription factor (11/12 positive, 92%), MelanA (14/16 positive, 88%), and S100 protein (2/10 positive, 20%). Of the smooth muscle markers, desmin was most commonly expressed (15/15 cases, 100%), followed by SMA (14/15 cases, 93%) and h-caldesmon (11/12 cases, 92%). TFE3 immunopositivity was identified in 5 of 13 cases; however, 3 tested cases were negative for a TFE3 rearrangement by fluorescence in situ hybridization. Current criteria for malignancy appear to be valid in the female genital tract, although modified criteria, as described herein, may be more specific. Awareness of the characteristic features of PEComa is important to help distinguish it from epithelioid smooth muscle tumors and other mimics as PEComa may respond to unique chemotherapeutic regimens.

Aims: Recently, SOX17 has emerged as a promising biomarker for non‐mucinous Müllerian (ovarian and endometrial) carcinomas, demonstrating increased specificity in comparison to PAX8 while maintaining similar sensitivity. However, expression of SOX17 in mesonephric‐like adenocarcinoma (MLA), a carcinoma of the female genital tract with uncertain, but probably Müllerian histogenesis, remains unexplored. This study aims to address this gap. Methods and results: SOX17 immunohistochemistry was performed on whole tissue sections from 68 MLAs originating from the endometrium or ovary and seven cervical mesonephric carcinomas, as well as six mesonephric remnants/hyperplasias. Using a four‐tiered scoring system based on distribution and intensity of staining, 68% of MLA displayed a negative/low (< 10%) SOX17 expression pattern, which contrasts with the high expression observed in most Müllerian carcinomas. However, 22% of MLA demonstrated high SOX17 expression, similar to other endometrial and ovarian carcinomas. Similarly, five of seven (72%) mesonephric carcinomas of the cervix were SOX17‐negative, but two cases (28%) were positive. All mesonephric remnants/hyperplasias were SOX17 negative. Conclusions: The majority of MLA are negative or exhibit low SOX17 expression, in contrast to the diffuse and strong expression commonly seen in other types of Müllerian carcinoma. However, a subset of MLAs demonstrate high SOX17 expression. Therefore, absence of SOX17 staining is supportive for MLA when the differential includes another non‐mucinous Müllerian carcinoma. SOX17 may also be useful for differentiating mesonephric remnants/hyperplasias from Müllerian malignancies and benign Müllerian glandular lesions. [ABSTRACT FROM AUTHOR]

ObjectiveTo credential Stathmin 1 (STMN1) and p16(INK4A) (p16) as adjunct markers for the diagnosis of serous tubal intraepithelial carcinoma (STIC), and to compare STMN1 and p16 expression in p53-positive and p53-negative STIC and invasive high-grade serous carcinoma (HGSC).MethodsImmunohistochemistry (IHC) was used to examine STMN1 and p16 expression in fallopian tube specimens (n=31) containing p53-positive and p53-negative STICs, invasive HGSCs, and morphologically normal FTE (fallopian tube epithelium). STMN1 and p16 expression was scored semiquantitatively by four individuals. The semiquantitative scores were dichotomized, and reported as positive or negative. Pooled siRNA was used to knockdown p53 in a panel of cell lines derived from immortalized FTE and HGSC.ResultsSTMN1 and p16 were expressed in the majority of p53-positive and p53-negative STICs and concomitant invasive HGSCs, but only scattered positive cells were present in morphologically normal FTE. Both proteins were expressed consistently across multiple STICs from the same patient and in concomitant invasive HGSC. Knockdown of p53 in immortalized FTE cells and in four HGSC-derived cell lines expressing different missense p53 mutations did not affect STMN1 protein levels.ConclusionsThis study demonstrates that STMN1 and p16 are sensitive and specific adjunct biomarkers that, when used with p53 and Ki-67, improve the diagnostic accuracy of STIC. The addition of STMN1 and p16 helps to compensate for practical limitations of p53 and Ki-67 that complicate the diagnosis in up to one third of STICs.

Aims: Biphasic hyalinizing psammomatous (BHP) renal cell carcinoma (RCC) is a newly described emerging entity within the spectrum of papillary RCC in the WHO 2022 classification. Molecular analyses have discovered that BHP RCC consistently harbour somatic mutations in the neurofibromin 2 (NF2) gene. The NF2 gene product, merlin, is known to primarily function as a tumour suppressor. Merlin protein loss correlates closely with the presence of NF2 mutations in benign and malignant tumours arising in different sites. In the present study we explored the role of merlin immunohistochemistry (IHC) in tumours within the spectrum of BHP RCC to determine the diagnostic utility of this marker. Materials and Methods: We performed merlin IHC in 13 BHP RCC, 18 papillary RCC, 10 TFE3-translocation RCC, 15 TFEB-altered RCC (including 13 TFEB-rearranged and 2 TFEB-amplified), and 10 mucinous tubular and spindle cell carcinomas of unknown mutational status. Results: Unequivocal loss of merlin expression in >90% of the tumour cells was observed in 12/13 BHP-RCC (92%), with the remaining tumour demonstrating weak focal cytoplasmic expression in ~10% of the tumour. In contrast, merlin was diffusely or multifocally expressed in all papillary RCC, TFE3- translocation RCC, and TFEB-altered RCC, as well as in 70% of mucinous tubular and spindle carcinomas. Conclusions: In this study, merlin IHC was ~92% sensitive and ~94% specific for BHP RCC. These data suggest that merlin IHC is a reliable surrogate marker for the presence of underlying NF2 gene inactivation, being diagnostically useful to identify BHP RCC. Conclusions: In this study, merlin IHC was ~92% sensitive and ~94% specific for BHP RCC. These data suggest that merlin IHC is a reliable surrogate marker for the presence of underlying NF2 gene inactivation, being diagnostically useful to identify BHP RCC. [ABSTRACT FROM AUTHOR]

Aims. Fumarate hydratase (FH)-deficient renal cell carcinoma (RCC) is a rare aggressive renal malignancy associated with hereditary leiomyomatosis and RCC syndrome (HLRCC). Tumors exhibiting heterogeneous (ie, patchy) FH loss by immunohistochemistry have rarely been described, may be diagnostically challenging, and have never been the focus of a study. We aimed to investigate the FH mutational status of FH-deficient RCC with heterogeneous versus complete FH loss, to characterize additional genetic drivers, and to evaluate 2SC immunohistochemistry in this setting. Methods and Results. We studied FH-deficient RCC with heterogeneous (n = 3) and complete (n = 4) FH loss. Targeted next-generation sequencing (NGS) was performed on all tumors. No patients had a known history of HLRCC. All tumors had histological features within the morphologic spectrum described for FH-deficient RCC. All 7 tumors were immunoreactive for 2SC. Molecularly, all 7 tumors revealed multiple hits involving the FH locus resulting in complete loss of wild-type alleles. All tumors with heterogeneous FH loss harbored FH missense variants within domain 2 of the protein, and each had concomitant copy neutral loss of heterozygosity (CN-LOH). In complete FH loss tumors, FH alterations included splice variants with concomitant loss of heterozygosity (n = 2) and homozygous gene deletions (n = 2). Other non-recurrent alterations included biallelic alterations of TP53, NF2, SMAD4 and activation of PIK3CA. Conclusions. Our series highlights how heterogeneous FH loss (patchy positive staining) is an important staining pattern to recognize since it is compatible with a diagnosis of FH-deficient RCC and should prompt additional ancillary studies (confirmatory 2SC immunohistochemistry and/or molecular testing) and genetic evaluation. [ABSTRACT FROM AUTHOR]

Aims: Mismatch repair (MMR) deficiency is commonly caused by functional inactivation of MLH1, PMS2, MSH2 or MSH6. The morphological and molecular correlates of MMR deficiency have been extensively characterized in certain tumour types such as colorectal and endometrial adenocarcinoma. In contrast, the histological and molecular features of MMR‐deficient prostate cancer remain incompletely described. In this study, we evaluated 19 MMR‐deficient prostate cancers, including 11 cases without prior systemic treatment. Methods and results: All treatment‐naive cases (11 of 11, 100%) were grade group 4–5 and had predominant cribriform and/or solid growth patterns. Solid components (any amount) and tumour infiltrating lymphocytes were 7 cases each (7 of 11, 64%). In 68 MMR‐proficient grade group 5 prostate cancers, predominant cribriform or solid growth patterns, solid components (any amount) and tumour infiltrating lymphocytes were seen at significantly lower frequencies (31 of 68, 46%; 9 of 68, 13% and 6 of 62, 9%, respectively; P < 0.001 for all comparisons). Molecular evaluation of 19 cases demonstrated that MMR‐deficiency was secondary to functional loss of MSH2/MSH6 and MLH1/PMS2 in 15 (79%) and 4 cases (21%), respectively. Definite or probable germline mutations were present in 4 cases (4 of 19, 21%). TMPRSS2::ERG rearrangements were identified in 2 cases (2 of 19, 11%). Recurrent cancer‐relevant somatic mutations included (but were not limited to) ATM, TP53, FOXA1, RB1, BRCA2 and PTEN. Conclusions: MMR deficiency was most commonly secondary to inactivation of MSH2/MSH6 in this study. Importantly, MMR‐deficient high‐grade prostatic adenocarcinomas had morphological features that might be useful to identify selected cases for MMR immunohistochemistry. [ABSTRACT FROM AUTHOR]

Fumarate hydratase (FH)-deficient renal cell carcinoma (RCC) is a rare and clinically aggressive RCC subtype that is commonly associated with the hereditary leiomyomatosis and renal cell carcinoma syndrome. The diagnostic hallmark of FH-deficient RCC is a high-grade microscopic appearance with prominent inclusion-like eosinophilic nucleoli and perinucleolar halos. Herein we report a case of an FH-deficient RCC in a 30-year-old female that exhibited low-grade nuclei and abundant eosinophilic cytoplasm, reminiscent of the clinically more indolent succinate dehydrogenase-deficient RCC subtype and the newly described eintity, eosinophilic, solid and cystic RCC. This case illustrates that FH-deficient RCC can have a wide spectrum of microscopic appearances, including low-grade eosinophilic RCC. In addition, it highlights that a low threshold to perform the immunohistochemical stains for FH and S-(2-succino) cysteine is warranted in RCC cases with unusual and even low-grade eosinophilic morphology. [ABSTRACT FROM AUTHOR]

Aims: Large cell calcifying Sertoli cell tumour (LCCSCT) is a rare testicular sex cord‐stromal tumour that primarily affects young patients and is associated with Carney complex. We sought to characterise the clinicopathological features of a series of LCCSCT and evaluate the diagnostic utility of PRKAR1A immunohistochemistry (IHC). Methods and results: The LCCSCT cohort (n = 15) had a median age of 16 years (range = 2–30 years). Four patients were known to have Carney complex. PRKAR1A IHC was performed in each case. For comparison, PRKAR1A IHC was also assessed in other sex cord‐stromal tumours, including Sertoli cell tumour, not otherwise specified (SCT, NOS; n = 10), intratubular large cell hyalinising Sertoli cell tumour (n = 1) and Leydig cell tumour (n = 23). Loss of cytoplasmic PRKAR1A expression was observed in all but one LCCSCT (14 of 15; 93%). PRKAR1A expression was retained in all SCTs, NOS (10 of 10; 100%), the majority of Leydig cell tumours (22 of 23; 96%) and an intratubular large cell hyalinising Sertoli cell tumour (1 of 1; 100%). One Leydig cell tumour showed equivocal staining (multifocal weak expression). Conclusions: Overall, PRKAR1A loss is both sensitive (93%) and highly specific (97%) for the diagnosis of LCCSCT. PRKAR1A loss may aid its diagnosis, particularly in sporadic cases and those that are the first presentation of Carney complex. [ABSTRACT FROM AUTHOR]

Aims: Renal epithelial neoplasms (RENs) can be difficult to subclassify, owing to overlapping morphological features. Carbonic anhydrase 9 (CA9) is a common biomarker for clear cell renal cell carcinoma (CCRCC); however, the sensitivity and specificity across REN subtypes are less clear. The aim of this study was to investigate CA9 expression in RENs, especially those in the differential diagnosis with CCRCC and less common entities, to determine its reliability as a diagnostic biomarker. Methods and results: CA9 immunostaining was performed on 262 RENs, including 119 CCRCCs and 143 non‐CCRCC. Immunostaining was evaluated as negative (0%), rare (1+, 1–10%), focal (2+, 11–50%), or diffuse (3+, >50%). CCRCCs were 3+ CA9‐positive in 93% of cases; 4% were CA9‐negative. Sixty‐seven percent of papillary renal cell carcinomas (RCCs) were 1+/2+ CA9‐positive, whereas 33% were CA9‐negative. Chromophobe RCCs were nearly always CA9‐negative (93%), with 7% showing rare cell reactivity. Clear cell tubulopapillary RCCs (CCTPRCCs) were consistently 3+ CA9‐positive, but with a cup‐like staining pattern. Fifty‐three percent of Xp11.2 RCCs were CA9‐negative; however, 6% were 3+ CA9‐positive and 12% were 2+ CA9‐positive. Two of eight fumarate hydratase‐deficient RCCs were 3+ CA9‐positive. A small subset of the remaining RCCs showed rare to focal CA9 expression. All oncocytomas and eosinophilic solid and cystic RCCs were CA9‐negative. Conclusions: Overall, diffuse CA9 expression was identified in nearly all CCRCCs and in all CCTPRCCs (high sensitivity); however, CA9 was not entirely specific. At least focal CA9 expression can been seen in a subset of many RCCs, and such findings should be taken into consideration with other morphological, immunophenotypic and clinical findings. [ABSTRACT FROM AUTHOR]

In the article, the authors present their study to determine whether grading intraductal carcinoma of the prostate (IDC) changes the National Comprehensive Cancer Network (NCCN) risk categorization. In the research, an immunohistochemistry (IHC) was performed on all foci suggestive of IDC in prostate biopsies. Also mentioned is the collection of clinical data and prostate-specific antigen (PSA) levels to calculate NCCN risk categories.

Aims: SMAD4 (DPC4) is a tumour suppressor gene that is dysregulated in various tumour types, particularly pancreaticobiliary and gastrointestinal carcinomas. Corresponding loss of protein expression has been reported in approximately 50% of pancreatic and 25% of colonic adenocarcinomas. In the evaluation of carcinoma of unknown primary site, immunohistochemical loss of SMAD4 expression is often used to suggest pancreaticobiliary origin, but there are limited data on the spectrum of SMAD4 expression in carcinomas of other sites. This study evaluates the frequency of SMAD4 loss in a large cohort of carcinomas from diverse anatomical sites. Methods and results: Immunohistochemistry for SMAD4 was performed on tissue microarrays or whole tissue sections of 1210 carcinomas from various organs: gastrointestinal tract, liver, pancreas/biliary tract, lung, breast, thyroid, kidney, ovary and uterus. Expression was considered lost when there was complete absence of staining in tumour cell nuclei, in the presence of intact staining in non‐neoplastic cells. SMAD4 loss was seen in 58% of pancreatic adenocarcinomas, 27% of appendiceal adenocarcinomas, 19% of colorectal adenocarcinomas, 16% of cholangiocarcinomas, 10% of lung adenocarcinomas and <5% of oesophageal, breast, gastric and mucinous ovarian adenocarcinomas. All papillary thyroid, hepatocellular, non‐mucinous ovarian, endometrial and renal cell carcinomas showed intact SMAD4 nuclear expression. Conclusion: In addition to pancreaticobiliary, appendiceal and colonic tumours, SMAD4 loss is also seen in a small subset of other carcinomas, specifically breast, lung, oesophageal and gastric adenocarcinomas, all of which are typically CK7‐positive, similar to pancreaticobiliary carcinoma. Awareness of SMAD4 loss in these other carcinoma types is helpful in the evaluation of carcinomas of unknown or uncertain primary site. [ABSTRACT FROM AUTHOR]

Aims: Renal angiomyolipoma (AML) and perivascular epithelioid cell tumour (PEComa) are members of the microphthalmia‐associated transcription factor (MiTF) family of tumours. Traditionally, HMB45 and melan‐A have been used to diagnose these lesions; however, low sensitivity can make interpretation difficult. PNL2 is a sensitive and specific biomarker for epithelioid melanoma, and immunoreactivity has also been shown in small series of PEComas. This study was aimed at determining the utility of PNL2 in MiTF and non‐MiTF renal tumours. Methods and results: PNL2 immunostaining was performed on 196 tumours, including 40 MiTF renal tumours [AMLs, epithelioid AMLs, sclerosing PEComas, malignant PEComas, and Xp11.2 renal cell carcinomas (RCCs)] and 156 non‐MiTF renal tumours. HMB45, melan‐A and cathepsin K were also evaluated in a subset of MiTF tumours. Overall, 85% of AMLs and PEComas were positive for PNL2, as compared with 81%, 76% and 95% that were positive for HMB45, melan‐A, and cathepsin K, respectively. In 55% of cases, PNL2 stained more extensively than HMB45. PNL2 staining was more frequent than HMB45 (78%) and melan‐A (38%) staining in sclerosing and malignant PEComas (89%). All remaining renal tumours, except one melanocytic Xp11.2 RCC, were negative for PNL2. Conclusions: PNL2 has high sensitivity and specificity for AML and PEComas as compared with non‐MiTF renal tumours, and PNL2 appears to be a more useful biomarker for sclerosing and malignant PEComas. For cases that are limited in tissue quantity (i.e. core biopsies) and/or are morphologically suspicious for AML/PEComa, but negative or focally positive for HMB45 and melan‐A, PNL2 may be a useful adjunctive biomarker. [ABSTRACT FROM AUTHOR]

PAX8 is important for embryogenesis of the thyroid, Müllerian system, and upper urinary/renal tract, and expression of PAX8 has been described in carcinomas from each of these sites. The sensitivity and specificity of the polyclonal PAX8 antibody in a large cohort of epithelial tumors as well as lymphomas have been previously determined, the latter because polyclonal PAX8 is known to be immunoreactive in nonneoplastic B-cell lymphocytes which are often used as the positive internal control for immunohistochemistry. In this case report, PAX8 was a diagnostic clue for revising a previous diagnosis of unclassified high grade sarcoma to diffuse large B-cell lymphoma. This case report demonstrates a pitfall for PAX8 immunoreactivity and acts as a reminder that lymphoma should be included in the differential diagnosis of a PAX8 positive, epithelial cell marker negative tumor of unknown primary origin. [ABSTRACT FROM AUTHOR]

Aims: Residual cancer morphology in radical prostatectomies (RPs) after neoadjuvant hormone therapy includes inconspicuous cytology, and treated tumour cells can be difficult to identify in lymph nodes. The aim of this study was to evaluate the role of immunohistochemistry (IHC) in identifying occult lymph node metastases following neoadjuvant hormone treatment of prostate cancer. Methods and results: One hundred and twenty-eight lymph nodes from 24 patients treated with neoadjuvant hormone therapy, including abiraterone acetate alone or combined with leuprolide, were stained with antibodies against keratin AE1/AE3, prostate-specific antigen (PSA), prostate-specific acid phosphatase (PrAP), androgen receptor (AR), and NKX3.1. IHC slides were scored 'blind', and then retrospectively compared with haematoxylin and eosin (H&E)-stained slides and pathology reports. IHC identified carcinoma in six lymph nodes from three patients. All metastases were positive for NKX3.1 and AR, five of six were positive for AE1/AE3, and three of six were positive for PSA; PrAP was negative in all metastatic foci. All six lymph node metastases had been identified by H&E staining at the time of RP. Conclusions: These findings suggest that routine use of IHC on lymph nodes from neoadjuvant-treated prostate carcinomas is not necessary. Nevertheless, for suspicious small foci of atypical cells in neoadjuvant- treated lymph nodes, NKX3.1 and AR appear to have the greatest sensitivity. [ABSTRACT FROM AUTHOR]

Aims GATA3 is a zinc-finger transcription factor that is important for trophoblast differentiation. GATA3 is sensitive for urothelial and breast carcinomas, but the specificity is low. The aim of this study was to investigate the expression of GATA3 in trophoblast-related tissues and neoplasia. Methods and results GATA3 immunohistochemistry was performed on 33 placentas, one atypical placental site nodule, 25 hydatidiform moles ( HMs), and 13 gestational trophoblastic tumours ( GTTs). One hundred and sixty endometrial adenocarcinomas were also stained. Western blotting was performed on trophoblastic cell lines and compared to other cancer cell lines. Immature placentas were characterized by strong, diffuse nuclear GATA3 staining. Mature placentas showed less expression with scattered positive cells in the villous cytotrophoblast. HMs showed diffuse expression in cytotrophoblast and implantation site trophoblast, and heterogeneous expression in extravillous trophoblast. All GTTs were positive for GATA3. All endometrial adenocarcinomas were GATA3-negative. Western blotting demonstrated GATA3 in choriocarcinoma, whereas the placenta, and cervical and endometrial cancer cell lines, were negative. Conclusions All trophoblast lineages were positive for GATA3. The extent of GATA3 expression varied between immature and mature placentas, suggesting a role in trophoblast maturation. GATA3 does not distinguish normal placenta, HMs, or GTTs. Nevertheless, GATA3 may help in distinguishing trophoblastic tumors from Mullerian epithelial malignancies and a subset of tumours of unknown origin. [ABSTRACT FROM AUTHOR]

Aims: The purpose of this study was to evaluate the expression patterns of B-cell specific activator protein (BSAP)/PAX5 and PAX8 in a wide variety of B-cell and T-cell neoplasms. Methods and results: A wide range of B-cell and T-cell neoplasms were subjected to immunohistochemical staining with antibodies against BSAP/PAX5 and PAX8 (polyclonal, pPAX8; monoclonal, mPAX8). Ten non-neoplastic lymph node specimens were examined with the same panel. All of the tested neoplastic and non-neoplastic B-cells reacted with the BSAP/PAX5 and pPAX8 antibodies, but did not show reactivity with the mPAX8 antibody. All tested T-cell neoplasms were negative using the BSAP/PAX5, pPAX8 and mPAX8 antibodies. Conclusions: This is the first study to show the absence of reactivity to an mPAX8 antibody in an expanded panel of B-cell lymphomas as well as in a variety of T-cell neoplasms. In contrast to the mPAX8 antibody, the pPAX8 antibody shows nuclear positivity in non-neoplastic B cells and mature B-cell neoplasms; however, this expression is probably a result of cross-reactivity with PAX5. Given that many laboratories use the pPAX8 antibody, a clear understanding of the differential staining patterns is necessary. The differential diagnosis of a B-cell lymphoma should be entertained when a pPAX8-positive, epithelial marker-negative neoplasm of uncertain primary origin is encountered. [ABSTRACT FROM AUTHOR]

Abstract: Pure morphological distinction of high-grade squamous intraepithelial lesions (HSILs) from their mimics can be challenging. Diagnosis can be difficult with nonconventional HSILs associated with a metaplastic phenotype, squamous intraepithelial lesions (SILs) that defy precise classification such as “eosinophilic dysplasias”, and those that overlap with columnar neoplasms, including stratified variants of adenocarcinoma in situ (“SMILE”). Gene expression and protein profiling have identified biomarkers with the potential to decrease diagnostic variability and increase specificity of histological and cytological analysis. Among the ones clinically useful for HSIL detection are p16INK4A and MIB-1 which complement each other, differentiating SIL from normal/atrophic (MIB-1 low) or reactive/immature metaplastic (p16INK4A scattered) epithelium. Additional markers, including ProEx™ C, have been proposed but their added value is yet to be established. In the final analysis, biomarkers are most helpful for distinguishing benign immature or atrophic proliferations from HSIL. The distinction of LSIL from HSIL must be made on the haematoxylin and eosin-stained section and should be made with care, given the potential consequences of a diagnosis of CIN2 or CIN3. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented regarding the use of BRAF V600E immunohistochemistry (IHC) to diagnose metanephric adenoma.

* Context.--Renal malignancies can be divided into cortical- and medullary-based tumors, the latter of which classically infiltrate the renal parenchyma by extending between nonneoplastic structures. Although high-grade cortical tumors can rarely exhibit the same growth pattern, the infiltrative morphology should elicit a differential diagnosis to be considered in each case. However, these diagnoses can be challenging to distinguish, especially on small renal biopsy samples. Objective.--To provide an overview of the clinical, gross, and microscopic findings; genetic and molecular alterations; and immunohistochemical evaluation of medullary- based renal tumors and other tumor types with overlapping morphologies and growth patterns. Data Sources.--Literature review and personal observations were used to compile the information in this review. Conclusions.--Collecting duct carcinoma is a prototypical medullary-based tumor, and although diagnostic criteria exist, it remains a diagnosis of exclusion, especially with ancillary techniques aiding the recognition of established as well as more recently described neoplasms. Other medullary-based malignancies included in the differential diagnosis include renal medullary carcinoma/ renal cell carcinoma unclassified with medullary phenotype, fumarate hydratase--deficient renal cell carcinoma, and upper tract urothelial carcinoma. Moreover, other rare entities should be excluded, including metastatic carcinoma, lymphoma, and melanoma. In addition to potential prognostic differences, accurate diagnoses can have important surgical and clinical management implications. [ABSTRACT FROM AUTHOR]

Abstract: Background: Due to concern that mucinous malignant or borderline ovarian neoplasms (MON) may represent metastatic deposits from appendiceal primaries, gynecologic oncologists routinely perform appendectomy in these cases. However, a multidisciplinary critique of this practice is lacking. Methods: The New England Case–Control study database was utilized to compare the effect of prior appendectomy against known risk factors for MON. Pathology and operative reports of local cases of MON were reviewed to estimate the frequency of microscopic mucinous lesions in the appendix. Protein expression patterns among mucinous ovarian, colorectal, and appendiceal cancers were compared by immunohistochemistry. Results: From the New England Case–Control study, 287 cases of MON were compared against 2339 age-matched controls. Prior appendectomy did not reduce the risk of MON (OR 1.28, 95% CI 0.83–1.92, p=0.23), while prior tubal ligation, parity, and breastfeeding were each protective against MON. Active smoking (OR 2.04, 95% CI 1.48–2.80, p<0.001) was associated with an increased risk of MON. Among 196 mucinous adnexal tumors, appendectomy did not reclassify any MON as appendiceal in origin. By immunohistochemistry, mucinous ovarian carcinomas tended to be CK7+/CK20−/MUC2−/CDX2−, whereas mucinous colorectal and appendiceal adenocarcinomas were typically CK7−/CK20+/MUC2+/CDX2+, although with some overlap in immunophenotype. Additionally, PAX8 was positive in a subset of MOC and negative in all appendiceal carcinomas. Conclusion: Prior appendectomy is not protective against development of malignant or borderline MON. Routine appendectomy during surgery for MON seldom reveals an unsuspected GI primary in early stage tumors but may aid in final diagnosis in advanced stage cases. Funding: National Cancer Institute grants P50-CA105009 and R21 CA-156021; The Honorable Tina Brozman ‘Tina's Wish’ Foundation; the Dr. Miriam and Sheldon G. Adelson Medical Research Foundation (AMRF); Dana-Farber Cancer Institute — Susan Smith Center for Women's Cancers; Robert and Deborah First Fund; The Gamel Family Fund; Mary Kay Foundation; Sandy Rollman Ovarian Cancer Foundation; Arthur Sachs/Fulbright/Harvard; La Fondation Philippe; La Fondation de France. [Copyright &y& Elsevier]

Abstract: Background: Metanephric adenoma (MA) of the kidney is a rare, indolent tumor that may be difficult to differentiate from other small renal masses (SRMs). Genetic alterations associated with MA remain largely unknown. Objective: We aimed at defining genetic events in MA of the kidney and determining their influence in the management of this disease. Design, setting, and participants: Multiplexed mass spectrometric genotyping was performed on 29 MA cases after tumor DNA extraction. We also conducted a mutational screen in an additional 129 renal neoplasms. Immunohistochemistry was performed on the MA cases to assess molecular markers of signaling pathway activation. Patients’ baseline characteristics, as well as follow-up data, were captured. Outcome measurements and statistical analysis: We used descriptive statistics for baseline clinical characteristics and incidence of mutations. The Wilcoxon rank-sum test was used to correlate patient characteristics with mutational status. Results and limitations: We identified the v-raf murine sarcoma viral oncogene homolog B1 (BRAF) V600E mutation in 26 of 29 MA cases. These results were validated in all cases using the commercially available BRAF Pyro Kit (QIAGEN). In contrast, BRAF mutations were rare in the other 129 non-MA renal neoplasms that were screened. We detected a BRAF mutation (V600E) in only one papillary renal cell carcinoma case. In all MA tumors, we documented expression of phosphorylated mitogen-activated protein kinase and phosphorylated extracellular signal–regulated kinase, accompanied by immunoreactivity for p16 (INK4a). All patients were treated with a partial or radical nephrectomy, and after a median follow-up of 26.5 mo, there were no local or distant recurrences. Limitations include the retrospective nature of this study. Conclusions: BRAF V600E mutations are present in approximately 90% of all MA cases, serving as a potential valuable diagnostic tool in the differential diagnosis of SRMs undergoing a percutaneous biopsy. The presence of BRAF V600E and mitogen-activated protein kinase activation in a largely benign tumor supports the necessity for secondary events (eg, p16 loss) in BRAF-driven oncogenesis. [Copyright &y& Elsevier]

Abstract: Background: Most high-grade pelvic serous carcinomas (HGPSCs) arise from fallopian tube epithelium (FTE). To date, few markers have been shown to characterize FTE transformation. Stathmin 1 (STMN1) is a candidate oncogene whose activity is influenced by p53, p27Kip1 (p27), and PI3K/Akt pathway activation. As a microtubule destabilizing protein, STMN1 regulates cytoskeletal dynamics, cell cycle progression, mitosis, and cell migration. This study examines the expression of STMN1 and its negative regulator p27 along the morphologic continuum from normal FTE to invasive carcinoma. Methods: STMN1 and p27 expression were examined by immunohistochemistry (IHC) in benign (n =12) and malignant (n =13) fallopian tubes containing normal epithelium, morphologically benign putative precursor lesions (“p53 signatures”), potential transitional precursor lesions (“proliferative p53 signatures”), tubal intraepithelial carcinoma (TIC), and/or invasive serous carcinoma. STMN1 expression was further assessed in 131 late-stage HGPSCs diagnosed as primary ovarian and in 6 ovarian cancer cell lines by IHC and Western blot, respectively. Results: STMN1 expression was absent in benign FTE and infrequently detected in p53 signatures. However, it was weakly expressed in proliferative p53 signatures and robustly induced upon progression to TIC and invasive carcinoma, typically accompanied by decreased p27 levels. STMN1 was expressed in >80% of high-grade serous ovarian carcinomas and cell lines. Conclusions: STMN1 is a novel marker of early serous carcinoma that may play a role in FTE tumor initiation. Our data are consistent with a model by which STMN1 overexpression, resulting from loss of p27-mediated regulation, may potentiate aberrant cell proliferation, migration, and/or loss of polarity during early tumorigenesis. [Copyright &y& Elsevier]