Endometrial Neuroendocrine Carcinoma With Widespread Metastases: Diagnostic and Therapeutic Challenges in a Rare Malignancy.

Endometrial neuroendocrine carcinomas (NECs) are rare, aggressive malignancies with early metastatic potential and poor prognosis. We present the case of a 54-year-old woman who presented with thoracic back pain and lower extremity paresthesia. Imaging revealed a T1 compression fracture, additional spinal metastases, liver and lung lesions, a thickened endometrium, and a left adnexal mass. Tumor markers, including CA-125, CA 19-9, and CEA, were markedly elevated. Thoracic spine MRI confirmed spinal stenosis and metastatic involvement. She underwent urgent T1 laminectomy with C5-T3 fusion, followed by systemic therapy with carboplatin/paclitaxel plus pembrolizumab, and later transitioned to carboplatin/etoposide. Treatment was complicated by Clostridioides difficile infection and chemotherapy-induced leukopenia, and she received palliative spinal radiation for symptom control. Histopathology confirmed small-cell NEC with squamous differentiation; expert review favored a poorly differentiated/dedifferentiated endometrial carcinoma with neuroendocrine and squamoid features. This case illustrates an atypical initial presentation with neurologic deficits from spinal metastases, emphasizing the need for prompt recognition and multidisciplinary management.