DICER1-associated metastatic abdominopelvic primitive neuroectodermal tumor with an EWSR1 rearrangement in a 16-yr-old female

Ewing Sarcoma of the Female Genital Tract: Clinicopathologic Analysis of 21 Cases With an Emphasis on the Differential Diagnosis of Gynecologic Round Cell, Spindle, and Epithelioid Neoplasms

Ewing sarcoma is an uncommon neoplasm considered in the differential diagnosis of tumors with "small round cell" morphology, but its occurrence in the gynecologic tract has only been sporadically documented. Herein, we describe the largest cohort of Ewing sarcoma localized to the female genital tract to date, and emphasize their clinicopathologic resemblance to more common gynecologic neoplasms. Ewing sarcoma (n=21) was retrospectively identified from 5 institutions. The average patient age was 35 (range 6-61) years. Tumor sites included uterus (n=8), cervix (n=4), vulva (n=5), vagina (n=1), broad ligament (n=1), inguinal area (n=1), and pelvis (n=1). Nine of 18 cases in which slides were available for review demonstrated only classic round cell morphology, with the remainder showing a variable combination and prominence of variant ovoid/spindle or epithelioid appearance. Tumors showed diffuse membranous reactivity for CD99 (20/20) and were positive for NKX2.2 (8/8, diffuse) and cyclin D1 (7/7, of which 3/7 were patchy/multifocal and 4/7 were diffuse). They were negative for ER (0/6) and CD10 (0/6). Three cases were initially diagnosed as endometrial stromal sarcomas. EWSR1 rearrangement was confirmed in 20/21 by fluorescence in situ hybridization (n=15) and/or sequencing (n=8). Of the eight tumors that underwent sequencing, 6 harbored FLI1 , 1 ERG, and 1 FEV as the fusion partner. Of 11 patients with available follow-up, 5 died of disease, 1 developed lung metastases and 5 are alive with no evidence of disease. Ewing sarcoma of the gynecologic tract is a rare, aggressive entity that shares some morphologic and immunohistochemical features with other more common gynecologic neoplasms. In addition to the typical round cell appearance, variant spindled/ovoid to epithelioid morphology may also be observed and should prompt consideration of this entity with appropriate immunohistochemical and/or molecular studies.

NEUROECTODERMAL ELEMENTS ARE PART OF THE MORPHOLOGICAL SPECTRUM OF DICER1-ASSOCIATED NEOPLASMS

Many sarcomas with DICER1 pathogenic variants (PVs) exhibit a characteristic morphology, including a subepithelial layer of malignant mesenchymal cells, areas of rhabdomyoblastic differentiation and cartilaginous and/ or osseous elements. We report 5 DICER1-associated neoplasms (1 moderately to poorly differentiated Sertoli Leydig cell tumour and 4 sarcomas) containing variable amounts of neuroectodermal elements. The neoplasms predominantly involved or were in close proximity to the female genital tract (ovary, uterine corpus, abdominal and pelvic cavity) and occurred in females aged 14 months to 54 years. The neuroectodermal elements were characterised by solid and tubular/ rosette-like patterns and variable immunoreactivity with SALL4 and neuroendocrine markers. In some cases, the neuroectodermal component was focal while in others it was exclusive. In one case, the focal neuroectodermal component within an ovarian Sertoli Leydig cell tumour resulted in extraovarian metastasis. In reporting these cases, we suggest that neuroectodermal elements, including pure neuroectodermal tumours, are part of the morphological spectrum of DICER1-associated neoplasms. It is important that pathologists recognize that a neuroectodermal component (often admixed with other elements) may be a feature of such neoplasms. This will facilitate appropriate tumour and/ or germline testing which could lead to the identification of germline DICER1 PVs (DICER1 syndrome). Three of the patients we report were subsequently shown to have a germline DICER1 PV.

Phenotypic similarities within the morphologic spectrum of DICER1-associated sarcomas and pleuropulmonary blastoma: Histopathologic features guide diagnosis in the LMIC setting

Extrapulmonary DICER1-associated sarcomas (DS) can harbor morphological features overlapping with pleuropulmonary blastoma. We report three children with intracranial and genital tract sarcomas, suspected to have DS based on a heterogeneous yet defining combination of spindle-cell sarcomatous and blastemal morphology, with rhabdomyomatous differentiation. Foci of immature cartilage at diagnosis (n = 2/3) and increased neuroepithelial differentiation at recurrence (n = 1) were noted. Morphological suspicion prompted somatic testing at reference centers, confirming likely biallelic, loss-of-function, and "hotspot" missense DICER1 variants in all three tumors. This can serve as a model for this diagnosis in resource-limited settings and has implications for germline testing, surveillance, and tumor management.