Pleomorphic high grade endometrial stromal sarcoma with YWHAE gene amplification may be a novel variant with poor prognosis.

Endometrial stromal neoplasms are classified by the World Health Organization (WHO) into endometrial stromal nodule (ESN), low grade (LGESS), high grade (HGESS), and undifferentiated uterine sarcoma (UUS). HGESS is subclassified based on molecular findings, YWHAE or BCOR. The HGESS with YWHAE::NUTM2A/B (alias YWHAE::FAM22A/B) fusion usually have relatively monomorphic (as with most fusion-associated malignancies) rounded to epithelioid cells with eosinophilic cytoplasm, vesicular nuclei, nucleoli, and mitotic figures >10/10 HPF. We present a 66-year-old woman with post-menopausal bleeding found to have a heterogeneous solid-cystic uterine mass on CT who underwent total hysterectomy, bilateral salpingo-oophorectomy, omentectomy, and pelvic lymph node dissection. A 15.0×9.0 cm variegated uterine mass with hemorrhage and necrosis was identified. Histologically, the tumor was hypercellular with haphazard fascicles, microcysts, and tongue-like destructive myometrial invasion. Tumor cells exhibited marked pleomorphism and high mitotic activity with atypical mitotic figures. There was extensive cyclin-D1 and subset CD10 immunopositivity. FISH showed YWHAE amplification but without rearrangement. Interestingly, we found only two other reported cases of pleomorphic HGESS with YWHAE gene amplification upon review of 259 cases from cBioPortal database, one of which was reported as carcinosarcoma with heterologous elements. Of note, all three YWHAE amplified cases were diagnosed at high-stage and succumbed to disease within six months. Our case appears to be the third case of YWHAE-amplified pleomorphic HGESS, possibly a new variant of uterine sarcoma with aggressive biologic behavior that needs further evaluation. IJCEP