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Context.--A variety of uncommon malignant endometrial tumors can be challenging to diagnose because of overlapping morphology with more common entities. In some cases, immunohistochemical stains and/or molecular testing allow for more definitive diagnosis or prognostication. Objective.--To review classic morphologic features of uncommon endometrial tumors, pathologic features of these tumors and their mimics, and the evidence for use of immunohistochemistry and molecular testing in the diagnosis of these tumors. Data Sources.--University of Michigan (Ann Arbor) cases and review of pertinent literature about each entity. Conclusions.--Although each of these uncommon endometrial tumors has morphologic mimics, key histologic features, immunohistochemical stains, and molecular testing allow for accurate classification. doi: 10.5858/arpa.2023-0098-RA, Although endometrial carcinoma is a common gynecologic malignancy, (1) there is suboptimal interobserver reproducibility in the diagnosis of high-grade endometrial cancers (ECs). (2-5) Historically, risk has been determined based on [...]

* Context.--Differentiated vulvar intraepithelial neoplasia (dVIN) is a human papillomavirus-independent lesion with the potential for rapid progression to invasive squamous cell carcinoma (SCC). The histopathologic features of dVIN are diverse, have overlapping characteristics with lichen sclerosus (LS) and lichen simplex chronicus (LSC), and may be diagnosed by dermatopathologists or gynecologic pathologists because of the vulva's anatomic location. Objectives.--To identify the salient histopathologic features of dVIN, particularly those that predict progression to SCC, and to evaluate interobserver agreement in diagnosing dVIN within the same subspecialty and across subspecialties. Design.--One general surgical pathologist, 2 pathology-trained dermatopathologists, and 1 gynecologic pathologist blinded to the final diagnoses were asked to record 20 histopathologic features and to provide their final interpretations on cases of dVIN (n = 65), LS (n = 126), LSC (n = 112), and LS with LSC (n = 6). Results.--Interobserver agreement for the 4 diagnoses and 10 histopathologic features was moderate. Logistic regression analysis indicated that keratin pearls, basal pleomorphism, and basal layer disarray were independent variables for diagnosing dVIN (coefficients 1.95,1.97, and 0.91, respectively; P < .001) and progression to SCC (coefficients 1.96,1.20, and 1.08, respectively; P < .001). Conclusions.--There is no single histopathologic feature pathognomonic for dVIN; however, the presence of keratin pearls, basal pleomorphism, and basal layer disarray should raise high suspicion for dVIN and concurrent SCC. Expertise in both dermatologic and gynecologic pathology is beneficial for diagnosing dVIN. (Arch Pathol Lab Med. 2023;147:1431-1437; doi: 10.5858/arpa.2022-0088-OA), Differentiated vulvar intraepithelial neoplasia (dVIN) has been well accepted as a precursor lesion of human papillomavirus (HPV)-independent squamous cell carcinoma (SCC) of the vulva. (1,2) Recognition of dVIN and its [...]

* Context.--While the vast majority of cervical tumors consist of human papillomavirus (HPV)-related squamous cell carcinoma or adenocarcinoma, a subset of rare tumor types, frequently unrelated to HPV, does occur in this location. These tumors vary widely in prognostic and therapeutic implications, and accurate recognition is crucial to providing appropriate treatment. Some are benign or portend a favorable prognosis (adenoid basal carcinoma, ectopic prostate tissue), while others are frankly malignant lesions with a less favorable prognosis (adenoid cystic carcinoma, HPV-negative endocervical adenocarcinoma, mesonephric adenocarcinoma, clear cell carcinoma, small cell carcinoma, and adenosquamous carcinoma). Objective.--To review the morphologic features of uncommon cervical lesions, the utility of immunohistochemistry for distinction between these entities, and the clinical and prognostic implications of accurate diagnosis. Data Sources.--University of Michigan cases and review of the pertinent literature regarding the entities described. Conclusions.--Key morphologic and immunohistochemical features detailed herein will allow for the accurate distinction between these uncommon cervical lesions. Morphology is most useful in discriminating between the entities, as there is frequent immunohistochemical overlap between them; however, in rare instances immunohistochemistry can be useful in resolving the diagnosis. (Arch Pathol Lab Med. 2021;145:891-902; doi: 10.5858/arpa.2020-0327-RA), Cervical cancer, a disease that has rapidly declined in incidence owing to the advent of routine screening with the Papanicolaou test and high-risk human papillomavirus (HPV) testing, primarily consists of [...]

Objectives Fluorescence in situ hybridization (FISH) assays for the detection of chromosomal rearrangements involving TFE3 and TFEB are considered the gold standard for the diagnosis of MiTF family altered renal cell carcinoma (MiTF-RCC). We reviewed 801 clinical TFE3 / TFEB FISH assays performed at our tertiary-level institution between 2014 and 2023 on kidney tumors suspicious at the morphologic or biomarker level for MiTF aberrations. Methods We summarized and analyzed clinical information, TFE3 / TFEB FISH results, and available biomarker staining results in a cohort of 453 consecutive kidney tumor cases suspicious for MiTF-RCC. Results In total, 61 of 434 (14%) kidney tumors were confirmed for TFE3 translocation; 10 of 367 cases (2.7%) were confirmed for TFEB translocation. Since TFEB amplification interpretation was implemented in our service line, 20 of 306 cases (6.5%) were diagnosed with TFEB amplification. Importantly, TFE3 and TFEB rearrangements were never co-detected within the same kidney tumor. Patients with TFEB amplification were significantly older (P <.001) than patients with TFE3 or TFEB translocation. Kidney tumors with TFEB amplification were seen to be at least 3 times as common as those with TFEB translocation. Conclusions Clinical TFE3 / TFEB FISH assays successfully identified and confirmed rare MiTF-RCC with TFE3 and TFEB rearrangements. Although morphologic and biomarker features associated with a kidney tumor may be suggestive of MiTF-RCC, clinical TFE3 / TFEB FISH assays are crucial for a confirmation and definitive subclassification of patients with MiTF-RCC. [ABSTRACT FROM AUTHOR]

* Context.--Histiocytic sarcoma is a rare neoplasm of mature histiocytes with an aggressive clinical course that can arise de novo or from a low-grade B-cell lymphoma. In particular, chronic lymphocytic leukemia/small lymphocytic lymphoma is a very common malignancy in the Western hemisphere, and most cases of chronic lymphocytic leukemia/small lymphocytic lymphoma have an indolent course and behavior. However, 2% to 8% of chronic lymphocytic leukemia/small lymphocytic lymphoma cases transform. Histiocytic sarcomatous transformation is rare and portends poor prognosis.Objective.--To review the clinical features, morphology, and key points related to the differential diagnosis for histiocytic sarcoma. We discuss recent understanding of the biology underlying transformation.Data Sources.--University of Michigan case and review of pertinent literature about histiocytic sarcoma and morphologic differential diagnosis.Conclusions.--Histiocytic sarcoma is a rare histiocytic neoplasm that can arise as a result of trans-differentiation from low-grade B-cell lymphomas, and has a wide differential diagnosis including other histiocytic/dendritic cell neoplasms, myeloid neoplasms, lymphomas, melanoma, and carcinoma. However, some key morphologic and immunohistochemical features allow for accurate classification.(Arch Pathol Lab Med. 2018;142:1322-1329; doi: 10.5858/arpa.2018-0220-RA), Histiocytic sarcoma is a rare neoplasm of mature histiocytes, and is considered to be a true hematopoietic tumor. (1,2) It can present as a primary malignancy or, less commonly, a [...]

* Context.--Primary cutaneous follicle center lymphoma is a low-grade B-cell lymphoma that is limited to the skin at diagnosis. It has a differential diagnosis that includes systemic/nodal follicular lymphoma secondarily involving the skin; primary cutaneous diffuse large B-cell lymphoma leg type; reactive lymphoid hyperplasia; and primary cutaneous marginal zone lymphoma. Objective.--To review the clinical, morphologic, immunophenotypic, and genetic features of primary cutaneous follicle center lymphoma; its differential diagnosis; and the evidence that supports use of immunohistochemistry and genetic testing in the diagnosis and prognosis of this entity. Data Sources.--Pertinent literature regarding cutaneous B-cell lymphomas is summarized and University of Michigan cases are used to highlight characteristics of primary cutaneous follicle center lymphoma. Conclusions.--Primary cutaneous follicle center lymphoma is a low-grade B-cell lymphoma with distinctive features, although some cases may have elements that overlap with other lymphomas, complicating interpretation. (Arch Pathol Lab Med. 2018;142:1313-1321; doi: 10.5858/arpa.2018-0215-RA), By definition, primary cutaneous follicle center lymphoma (PCFCL) is a lymphoma of follicle center B cells without evidence of systemic/nodal involvement at the time of diagnosis. (1-5) It is a [...]

Context.--Hereditary leiomyomatosis and renal cell carcinoma syndrome (HLRCC) is an uncommon disorder with germline-inactivating mutations in the fumarate hydratase (FH) gene. The kidney cancers that develop in patients with HLRCC are often unilateral and solitary, with a potentially aggressive clinical course; morphologic identification of suspicious cases is of the utmost importance. Objective.--To review classic morphologic features of HLRCC-associated renal cell carcinoma, the reported morphologic spectrum of these tumors and their mimics, and the evidence for use of immunohistochemistry and molecular testing in diagnosis of these tumors. Data Sources.--University of Michigan cases and review of pertinent literature about HLRCC and the morphologic spectrum of HLRCC-associated renal cell carcinoma. Conclusions.--Histologic features, such as prominent nucleoli with perinucleolar halos and multiple architectural patterns within one tumor, are suggestive of HLRCC-associated renal cell carcinoma. However, the morphologic spectrum is broad. Appropriate use of FH immunohistochemistry and referral to genetic counseling is important for detection of this syndrome. doi: 10.5858/arpa.2018-0216-RA, Hereditary leiomyomatosis and renal cell carcinoma syndrome (HLRCC), also referred to as Reed syndrome, (1-4) is a rare familial cancer disorder caused by a germline mutation in the fumarate hydratase [...]

Introduction. Chromophobe renal cell carcinoma (chromophobe RCC) is the third major subcategory of renal tumors after clear cell RCC and papillary RCC, accounting for approximately 5% of all RCC subtypes. Other oncocytic neoplasms seen commonly in surgical pathology practice include the eosinophilic variant of chromophobe RCC, renal oncocytoma, and low-grade oncocytic unclassified RCC. Methods. In our recent next-generation sequencing based study, we nominated a lineage-specific novel biomarker LINC01187 (long intergenic non-protein coding RNA 1187) which was found to be enriched in chromophobe RCC. Like KIT (cluster of differentiation 117; CD117), a clinically utilized chromophobe RCC related biomarker, LINC01187 is expressed in intercalated cells of the nephron. In this follow-up study, we performed KIT immunohistochemistry and LINC01187 RNA in situ hybridization (RNA-ISH) on a cohort of chromophobe RCC and other renal neoplasms, characterized the expression patterns, and quantified the expression signals of the two biomarkers in both primary and metastatic settings. Results. LINC01187, in comparison to KIT, exhibits stronger and more uniform expression within tumors while maintaining temporal and spatial consistency. LINC01187 also is devoid of intra-tumoral heterogeneous expression pattern, a phenomenon commonly noted with KIT. Conclusions. LINC01187 expression can augment the currently utilized KIT assay and help facilitate easy microscopic analyses in routine surgical pathology practice. [ABSTRACT FROM AUTHOR]

Although papillary renal cell carcinoma has historically been classified as either type 1 or type 2, data from The Cancer Genome Atlas (TCGA) has demonstrated significant genomic heterogeneity in tumors classified as "type 2 papillary renal cell carcinoma" (T2PRCC). Papillary renal cell carcinoma is expected to have a favorable clinical course compared to clear cell renal cell carcinoma (CCRCC). However, tumors with poor outcome more similar to CCRCC were included in the T2PRCC cohort studied by the TCGA. The differential diagnosis for T2PRCC includes a variety of other renal tumors, including aggressive entities such as TFE3 translocation-associated renal cell carcinoma, TFEB-amplified renal cell carcinoma, fumarate hydratase-deficient renal cell carcinoma, high-grade CCRCC, and collecting duct carcinoma. Accurate classification of these tumors is important for prognostication and selection of therapy. [ABSTRACT FROM AUTHOR]

Aims: Distinction between well‐differentiated endometrial carcinoma (EMCA) with microglandular/mucinous features and benign endocervical microglandular hyperplasia (MGH) can be a diagnostic challenge, especially when tissue is limited. The immunostains used to distinguish endocervical and endometrial carcinoma are less useful when the differential diagnosis is MGH. Here, we investigate the utility of p63 and phosphatase and tensin homologue (PTEN) to aid accurate classification. Methods and results: Cases obtained from our pathology archives included 25 EMCA with mucinous/microglandular features, 26 MGH and nine atypical microglandular proliferations. Cases were assessed for glandular architecture, presence of mucinous and/or eosinophilic luminal secretions, subnuclear vacuoles, foamy histiocytes, inflammation, squamous metaplasia, cytological atypia and mitotic activity. The presence and pattern of immunohistochemical staining for p63 and PTEN was recorded. Microglandular proliferations with cytological atypia, mitotic activity, foamy histiocytes and complex glandular architecture were more commonly seen in EMCA, while small glands, bland nuclei and subnuclear vacuoles were enriched in MGH. All MGH cases displayed p63‐positive subcolumnar reserve cells and retained PTEN expression. Four EMCA cases showed non‐specific focal p63 staining either at the surface of the tumour or in areas of squamous differentiation. p63 and PTEN immunostains accurately predicted the final diagnosis for 3 atypical microglandular proliferation cases with follow‐up. Conclusions: While there are morphological characteristics that differentiate EMCA and MGH, there is frequent overlap between these entities. Nonetheless, the pattern and extent of p63 and PTEN can aid accurate classification. Consistent p63‐positive subcolumnar reserve cells were seen only in MGH. [ABSTRACT FROM AUTHOR]

Aims: As gender‐affirming surgery is becoming more common, it is important for pathologists to recognize potential benign findings to avoid misinterpretation. Cervical transitional cell metaplasia and superficial clusters of small basophilic cells have been described in the context of gender‐affirming testosterone therapy; these findings may be misdiagnosed as high‐grade squamous intraepithelial lesions or endometrial cells on Pap smears. Prostatic metaplasia has been reported in the surface squamous epithelium of the vagina and the uterine cervix in individuals undergoing gender‐affirming androgen therapy; this finding is often associated with NKX3.1‐positive basal keratinocytes. The aim of this study was to assess the morphological and immunohistochemical features of the uterine cervix in gender‐affirming hysterectomies in comparison with benign hysterectomies from cisgender women. Methods and results: We assessed the morphological and immunohistochemical features of the uterine cervix in 49 gender‐affirming hysterectomies as compared with 57 hysterectomies from cisgender patients to establish the relative prevalences of surface prostatic metaplasia, NKX3.1‐positive basal keratinocytes, transitional cell metaplasia, and small basophilic cells in the cervical squamous epithelium. The cervical tissue from the gender‐affirming therapy cohort showed significantly higher prevalences of NKX3.1‐positive basal keratinocytes (86% versus 1.8%), transitional cell metaplasia (80% versus 3.5%), superficial clusters of small basophilic cells (67% versus 7%), and surface prostatic metaplasia (43% versus 3.5%). Conclusion: NKX3.1‐positive basal keratinocytes, transitional cell metaplasia, small basophilic cells and surface prostatic metaplasia are all more prevalent in the cervices of individuals receiving gender‐affirming testosterone therapy; awareness of this fact allows pathologists to avoid the overdiagnosis of dysplasia or the recommendation of unnecessary follow‐up procedures. [ABSTRACT FROM AUTHOR]

Aims: Atypical polypoid adenomyoma (APAM) is an uncommon uterine lesion composed of complex endometrioid glands with frequent squamous morular metaplasia and fibromuscular stroma. On endometrial curettage, biopsy or polypectomy specimens, the admixture of endometrioid glands and smooth muscle raises the differential diagnosis of myoinvasive endometrioid carcinoma. Reproductive‐age APAM patients may opt for fertility preservation, whereas myoinvasive carcinoma is treated surgically. One previous study reported an incidental finding that the stroma of APAM, in contrast to that of other polypoid lesions, was SATB2‐positive. APAM has also been reported to show increased stromal p16 staining. We aimed to assess whether SATB2 and p16 are useful stains for the distinction of APAM from myoinvasive carcinoma and benign adenomyomatous polyps. Methods and results: Cases of 'atypical polypoid adenomyoma' (n = 32), 'adenomyomatous polyp' (n = 39) and 'myoinvasive endometrioid carcinoma' (n = 30) were identified. Morphological features were assessed, along with the intensity and extent of SATB2 and p16 staining in the stromal component of each lesion. SATB2 expression was seen in the stromal components of 30 of 32 (94%) APAMs, versus none of 39 (0%) benign adenomyomatous polyps and five of 30 (17%) myoinvasive endometrioid carcinomas. Stromal p16 expression was seen in 31 of 31 (100%) APAMs, versus 20 of 39 (51%) benign adenomyomatous polyps and 12 of 30 (40%) myoinvasive endometrioid carcinomas. Conclusions: Patchy to diffuse SATB2 and block‐type p16 staining of fibromuscular stroma separating atypical endometrioid glands is more consistent with APAM than with myoinvasive endometrioid carcinoma. These stains are potentially useful adjuncts to careful morphological evaluation of endometrial biopsies/curettings. [ABSTRACT FROM AUTHOR]

Follicle center lymphomas, including primary cutaneous follicle center lymphoma (PCFCL), may rarely show plasmacytic differentiation. Such cases can pose a diagnostic challenge and can be mistaken for other lymphomas that more commonly include plasma cells. Here, we report four cases of PCFCL and one case of systemic follicular lymphoma involving the skin with associated monotypic plasma cells, including the clinical, morphologic and immunophenotypic features. [ABSTRACT FROM AUTHOR]

Renal cell carcinomas (RCCs) are a heterogeneous group of neoplasms. Recent sequencing studies revealed various molecular features associated with histologic RCC subtypes, including chromophobe renal cell carcinoma (ChRCC). To characterize the gene expression and biomarker signatures associated with ChRCC. We performed integrative analysis on RNA sequencing data available from 1049 RCC specimens from The Cancer Genome Atlas and in-house studies. Our workflow identified genes relatively enriched in ChRCC, including Forkhead box I1 (FOXI1), Rh family C glycoprotein (RHCG), and LINC01187. We assessed the expression pattern of FOXI1 and RHCG protein by immunohistochemistry (IHC) and LINC01187 mRNA by RNA in situ hybridization (RNA-ISH) in whole tissue sections representing a cohort of 197 RCC cases, including both primary and metastatic tumors. The FOXI1 and RHCG IHC staining, as well as the LINC01187 RNA-ISH staining, was evaluated in each case for intensity, pattern, and localization of expression. All primary and metastatic classic ChRCCs demonstrated homogeneous positive labeling for FOXI1, RHCG proteins, and LINC01187 transcript. Unclassified RCC with oncocytic features, oncocytoma, and hybrid oncocytic tumor, as well as all but two cases of eosinophilic ChRCC also stained positive. Importantly, metastatic and primary RCC of all other subtypes did not demonstrate any unequivocal staining for FOXI1, RHCG, or LINC01187. In normal kidney, FOXI1, RHCG, and LINC01187 were detected in the distal nephron segment, specifically in intercalated cells. Two cases of eosinophilic ChRCC with focal expression of FOXI1 and LINC01187 , and Golgi-like RHCG staining were found to contain MTOR gene mutations upon DNA sequencing. We demonstrate a pipeline for the identification and validation of RCC subtype–specific biomarkers that can aid in the confirmation of cell of origin and may facilitate accurate classification and diagnosis of renal tumors. FOXI1 , RHCG , and LINC01187 are lineage-specific signature genes for chromophobe renal cell carcinoma. We performed integrative RNA sequencing analysis from >1000 renal cell carcinoma (RCC) specimens, identified genes enriched in chromophobe RCC, experimentally validated the expression pattern of the top three genes (FOXI1 , RHCG , and LINC01187), and revealed that the cell of origin of chromophobe RCC is intercalated cells. [ABSTRACT FROM AUTHOR]

We report an index case of histiocytic sarcoma arising in a 70-year-old patient with long-standing chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL). The patient presented in 2017 with painful, enlarging swelling of the left neck. He had remote history of cutaneous squamous cell carcinoma with no sign of recurrence, and his CLL/SLL was thought to be in remission. Computed tomography showed mild splenomegaly and multifocal lymphadenopathy including a 3-cm left neck mass. Biopsy of the left neck mass showed CLL/SLL with associated histiocytic sarcoma. Flow cytometry demonstrated a B cell neoplasm with CLL/SLL phenotype. Despite radiation therapy, he expired 3 months after presentation. Two similar cases (CLL/SLL and histiocytic sarcoma, follicular lymphoma and Langerhans cell sarcoma) from another institution are also illustrated. The pathological features of combined tumors in lymphoid neoplasms, a general framework to the work-up to determine interrelatedness of tumor components, and the clinical relevance are discussed. [ABSTRACT FROM AUTHOR]