Collision Tumor of Endometrial Large Cell Neuroendocrine Carcinoma and Low-Grade Endometrial Stromal Sarcoma: A Case Report and Review of the Literature.

Large cell neuroendocrine carcinoma (LCNEC) of the endometrium is an exceedingly rare histologic subtype of endometrial cancer (0.8%). These tumors are highly aggressive with a propensity for metastasis and have a poor prognosis. Among the 17 cases reported to date, 9 cases were pure large cell neuroendocrine tumors and 8 were collision tumors of LCNEC with endometrial carcinomas (7 endometrioid and 1 serous). In this article, we report a case of collision tumor composed of an endometrial LCNEC and a low-grade endometrial stromal sarcoma (LGESS). The patient was a 48 year-old woman who presented with a large abdominal mass for about 10 years and underwent total hysterectomy, bilateral salpingo-oophorectomy, and tumor debulking. Microscopic evaluation demonstrated an LGESS with extensive osseous metaplasia that penetrated through the myometrium and invaded into pelvic and abdominal cavity, forming a 40.0-cm mass. Cytogenetic analysis of the LGESS revealed an abnormal female karyotype (45, XX) with multiple structural abnormalities. Incidentally, small foci of LCNEC were identified within the endometrium. The LCNEC focally invaded the myometrium with involvement of the endocervix, extensive lymph-vascular space invasion, and metastases to bilateral ovaries. Subsequently, the patient was treated with cisplatin/etoposide chemotherapy and had been doing well for about a year until presenting with recurrence of LCNEC in the abdomen. She passed away a month later due to medical complications. This report reveals an extremely rare endometrial collision tumor with unusual pathologic features and clinical presentations.