Evaluation of fluorescence in-situ hybridization in monomorphic endometrial stromal neoplasms and their histological mimics: a review of 49 cases

AimsTo perform a population-based review of monomorphic endometrial stromal tumours and their histological mimics presenting over a 20-year period, including an evaluation of fluorescence in-situ hybridization (FISH) for the JAZF1 and YWHAE breakaparts. Methods and resultsForty-nine tumours were examined, comprising 13 histological mimics and 36 endometrial stromal tumours [six stromal nodules (ESNs), 25 low-grade stromal sarcomas (ESSs), and five monomorphic undifferentiated sarcomas (mUESs)]. Nine ESSs showed variant histological patterns, including smooth muscle, sex cord-like/glandular, fibrous or rhabdoid differentiation. Three ESSs were initially misclassified as benign uterine lesions, and, conversely, three benign mimics were originally reported as ESSs. One mUES showed a prominent pseudopapillary pattern. Fluorescence in-situ hybridization demonstrated JAZF1 breakaparts in five of six ESNs and 16 of 25 ESSs; however, only three of nine ESS variants were positive. YWHAE breakaparts were present in four of five mUESs. Analysis of a subsequent metastasis in the YWHAE breakapart-negative mUES demonstrated a YWHAE deletion. None of the histological mimics was positive in FISH analysis. Diffuse cyclin D1 expression was restricted to mUESs in this series. ConclusionsEndometrial stromal neoplasms continue to present diagnostic difficulty. Fluorescence in-situ hybridization analysis is helpful in distinguishing stromal tumours from their histological mimics and in distinguishing ESS from mUES.