Pure Large Cell Neuroendocrine Carcinoma Originating from the Endometrium: A Case Report and Review of Literature.

Large cell neuroendocrine carcinoma (LCNEC) of the endometrium is a rare and aggressive high-grade malignancy, constituting fewer than 1% of endometrial malignancies, with only 33 cases reported in the literature to date. We present the case of a 66-year-old multiparous postmenopausal woman with a previous history of invasive breast carcinoma, managed with mastectomy, chemotherapy, and hormone treatment. The patient presented with vaginal bleeding and leukorrhea. Magnetic resonance imaging revealed endometrial thickening with myometrial and parametrial invasion, and positron emission tomography/computed tomography revealed no evidence of nodal or distant metastases. The pipelle biopsy revealed poorly differentiated cancer. She underwent a robotic hysterectomy, bilateral salpingo-oophorectomy, sentinel lymph node biopsy, omental biopsy, and peritoneal cytology procedures. The histopathological analysis verified a pure LCNEC and was staged as pT2N0M0. Immunohistochemistry showed positivity for synaptophysin, CD56, chromogranin, and p53 (mutant), weak positivity for EMA, and a Ki-67 index of 80%. The tumor exhibited microsatellite stability, and next-generation sequencing revealed no relevant mutations. She received adjuvant therapy with pelvic radiation with concurrent cisplatin, followed by vaginal brachytherapy, and four cycles of chemotherapy with carboplatin and etoposide. This case demonstrates favorable outcomes with multimodal therapy, emphasizing the importance of timely management of this rare entity.