The treatment challenges of an exceedingly rare diagnosis of rectal small cell neuroendocrine carcinoma: a case report

Small cell neuroendocrine carcinoma (SCNEC) of the rectum is a rare, aggressive malignancy with limited evidence guiding management. We report a case of T4N1b rectal SCNEC in a female presenting with severe proctalgia. Imaging and endoscopy identified a near-obstructing rectal mass, with histology confirming SCNEC. Staging demonstrated locoregional disease without distant metastases. Initial management with platinum-based chemotherapy, etoposide, and radiotherapy achieved partial response; however, persistent disease abutting the posterior vaginal wall necessitated abdominoperineal resection (APR) with partial vaginectomy. Histology revealed poor treatment response and close margins, indicating high recurrence risk. She underwent close surveillance, ultimately progressing to metastatic disease 8 months later, and underwent further adjuvant chemotherapy and immunotherapy. She was eventually palliated with continued deterioration secondary to febrile neutropaenia and myelodysplastic syndrome, ultimately passing away a further 2 months later. This case highlights the aggressive nature of rectal SCNEC, uncertainty surrounding optimal management, and the need for flexible, multidisciplinary approaches. Further research is required to establish evidence-based disease specific treatment algorithms for a diagnosis that is void of such definitive guidelines and treatment strategies which are largely extrapolated.