Julia A. Bridge

Axillary lymph nodes are a common site of metastatic carcinoma, particularly from the breast. Epithelial inclusions within axillary lymph nodes are uncommon but well recognized, most frequently encountered as small, incidental clusters of mammary-type epithelium; squamous, Müllerian, and mixed types are also sporadically identified. Hidradenoma is a benign adnexal neoplasm classically composed of epidermoid/squamoid, intermediate/basaloid, and mucinous cells that most commonly originates in the skin but can arise in the breast parenchyma, with morphologic and genetic features that overlap with mucoepidermoid carcinoma. Rare instances of hidradenomas within pelvic and axillary lymph nodes have been reported, raising the specter of metastasis. We report 3 cases of axillary lymph node hidradenoma presenting without a concurrent breast or cutaneous lesion. Morphology, immunohistochemistry, and molecular studies were evaluated. Two cases were found to harbor CRTC1::MAML2 rearrangements, while a rarer CRTC3::MAML2 fusion was identified in a third case. Following excision, the 3 patients were without evidence of residual disease, with clinical follow-up of ∼2 years each. Recognition of this entity is essential to avoid misclassification as metastatic carcinoma and prevent overtreatment.

Introduction: Teratomas are the most common germ cell tumours in the gynaecological tract, the vast majority arising in the ovary. Limited information is available on uterine teratomas. Methods: We evaluated clinicopathological features of five uterine teratomas, fluorescence in situ hybridization for isochromosome 12p [i(12p)], short tandem repeat (STR) analysis, and targeted DNA sequencing in a subset. Results: Patients' age ranged from 29 to 60 (median: 40) years. Three underwent hysterectomy and two conservative cervical excisions. All tumours were uterine confined with four centred in the cervix and one in the corpus, ranging from 2.4 to 6.5 (median: 3.75) cm. Three tumours only had mature elements with one associated with mature glial tissue in the peritoneum and endometrium. The other two tumours also showed immature neural tissue, warranting a diagnosis of Grade 2 immature teratoma based on ovarian criteria. Four patients were alive with no evidence of disease with median follow‐up of 13 (range 2–42) years. i(12p) was not detected in two tumours with available material (one mature and one immature). STR analysis showed heterozygosity in one mature and complete homozygosity in one immature teratoma. Targeted DNA sequencing revealed no pathogenic or likely pathogenic alterations in one immature teratoma and a pattern consistent with genome‐wide loss of heterozygosity. Conclusions: Uterine teratomas display either mature or an admixture of mature and immature elements and can rarely be associated with gliomatosis. Limited data show no association with i(12p). The malignant potential of immature uterine teratomas is not well established and they appear to be more akin to sacrococcygeal than ovarian teratomas based on limited STR results from this cohort and the literature.

Dermatofibrosarcoma protuberans (DFSP) is a locally infiltrative mesenchymal neoplasm usually characterized by a COL1A1::PDGFB fusion. A minority of DFSPs have recently been shown to harbor alternative fusions, involving the PDGFD gene. The aim of this case series and literature review is to highlight the clinicopathologic and molecular features of PDGFD-rearranged DFSPs. Eighteen patients (twelve females and six males) with PDGFD-rearranged DFSPs were collected from the authors’ institutional archives. Eight (44%) cases harbored a COL6A3::PDGFD fusion, five (28%) an EMILIN2::PDGFD fusion, and two (11%) an EMILIN1::PDGFD fusion. In three (17%) cases, the fusion partner was unknown. A literature review revealed 29 additional cases. Cumulatively, four alternative fusion genes have been detected: COL6A3::PDGFD (24/47, 51%), EMILIN2::PDGFD (12/47, 26%), EMILIN1::PDGFD (2/47, 4%), and TNC::PDGFD (1/47, 2%). In eight (17%) cases, the fusion partner was unknown. Most (20/24, 83%) COL6A3::PDGFD-fused DFSPs occurred in females with only four (17%) cases described in males. Additionally, half of them (12/24, 50%) developed in the breast/chest wall. EMILIN2::PDGFD-fused DFSPs often occurred in males, were located in the extremities (9/12, 75%), exhibited fibrosarcomatous transformation (9/12, 75%), were confined exclusively or primarily to the subcutis (10/12, 83%), and had a well-circumscribed contour (10/12, 83%). Specific molecular alterations in DFSPs correlate with certain clinicopathologic features. Notably, EMILIN2::PDGFD-fused DFSPs have a slight predilection for males, develop almost exclusively in the subcutis, tend to be well-circumscribed, and often exhibit fibrosarcomatous transformation, while COL6A3::PDGFD-fused DFSPs might have a predilection for the breast/chest wall of female patients. To the best of our knowledge, this is the first report of EMILIN1::PDGFD-fused DFSP.

Context: Next-generation sequencing–based approaches using RNA have increasingly been used by clinical laboratories for the detection of fusion genes, intragenic rearrangements, and exon-skipping events. Correspondingly, the College of American Pathologists (CAP) has advanced RNA sequencing proficiency testing (PT) to ensure optimal performance of these assays. Objective: To report on laboratory performance and practices of RNA sequencing for the detection of fusion genes, intragenic rearrangements, and exon-skipping events using CAP PT data from 8 mailings (2018-A through 2021-B). Design: CAP PT RNA sequencing program results from 153 laboratories across 24 proficiency test specimens, interrogating 22 distinct engineered fusion transcripts, were analyzed for correct identification of the fusion event, associated performance variables, and laboratory practices. Results: Overall, the 4-year program detection rate (sensitivity) was 95.5% (1486 of 1556 results). False-negative rates were 3.6% (53 of 1463) and 18.3% (17 of 93) for fusion gene and intragenic rearrangement/exon-skipping events, respectively. Only 19 false-positive results were reported among the 8 PT mailings, and most were likely the result of preanalytical or postanalytical errors. There were no practice characteristics (eg, instrumentation, sequencing method) significantly associated with the fusion detection results. Conclusions: These data reveal a high overall sensitivity and specificity for fusion gene detection by participating laboratories using clinical RNA sequencing. Performance was comparable across all laboratories, regardless of methodology. The fraction of false-negative results for intragenic rearrangement/exon-skipping events was greater than that for the chimeric fusion genes. False-negative results could not be attributed to any specific practice characteristics.

Pseudomyogenic hemangioendothelioma, an uncommon mesenchymal neoplasm composed of plump spindled and/or epithelioid endothelial cells, may present multicentrically and tends to locally recur but rarely metastasizes. Morphologic resemblance to epithelioid sarcoma and other spindle cell neoplasms may result in diagnostic confusion. Molecular characterization of pseudomyogenic hemangioendothelioma has revealed these neoplasms often harbor a rearrangement of the FOSB gene with SERPINE1 or ACTB as recurrent fusion gene partners. Herein, a case of a fibular pseudomyogenic hemangioendothelioma with minimal extension into the adjacent soft tissue arising in a 17 year‐old male is presented. The neoplasm exhibited sheets of epithelioid cells with abundant eosinophilic cytoplasm and variably eccentric nuclei. RNA sequencing revealed a novel CLTC‐FOSB fusion transcript that was subsequently confirmed by direct sequencing of reverse transcription‐polymerase chain reaction products demonstrating an in‐frame fusion between exon 17 of the clathrin heavy chain (CLTC) gene and exon 2 of the FOSB (FosB proto‐oncogene, AP‐1 transcription factor subunit) gene. CLTC‐FOSB fusion has not been described in a neoplasm before.

Despite suboptimal sensitivity urine cytology is often performed as an adjunct to cystoscopy for bladder cancer diagnosis. We aimed to develop a noninvasive, fast molecular diagnostic test for bladder cancer detection with better sensitivity than urine cytology while maintaining adequate specificity. Urine specimens were collected at 18 multinational sites from subjects prior to cystoscopy or tumor resection, and from healthy and other control subjects without evidence of bladder cancer. The levels of 10 urinary mRNAs were measured in a training cohort of 483 subjects and regression analysis was used to identify a 5-mRNA model to predict cancer status. The performance of the GeneXpert® Bladder Cancer Assay, an assay labeled for investigational use only to detect the 5 mRNAs ABL1, CRH, IGF2, ANXA10 and UPK1B, was evaluated in an independent test cohort of 450 participants. In the independent test cohort the assay ROC curve AUC was 0.87 (95% CI 0.81-0.92). At an example cutoff point of 0.4 overall sensitivity was 73% while specificity was 90% and 77% in the hematuria and surveillance patient populations, respectively. We developed a 90-minute, urine based test that is simple to perform for the detection of bladder cancer. The test can help guide physician decision making in the management of bladder cancer. Additional evaluation in a prospective study is needed to establish the clinical usefulness of this assay.

The introduction of molecular testing into cytopathology laboratory practice has expanded the types of samples considered feasible for identifying genetic alterations that play an essential role in cancer diagnosis and treatment. Reverse transcription–polymerase chain reaction (RT‐PCR), a sensitive and specific technical approach for amplifying a defined segment of RNA after it has been reverse‐transcribed into its DNA complement, is commonly used in clinical practice for the identification of recurrent or tumor‐specific fusion gene events. Real‐time RT‐PCR (quantitative RT‐PCR), a technical variation, also permits the quantitation of products generated during each cycle of the polymerase chain reaction process. This review addresses qualitative and quantitative pre‐analytic and analytic considerations of RT‐PCR as they relate to various cytologic specimens. An understanding of these aspects of genetic testing is central to attaining optimal results in the face of the challenges that cytology specimens may present. Cancer Cytopathol 2017;125:11‐19. © 2016 American Cancer Society.