Successful outcome achieved with adjuvant chemotherapy with irinotecan plus cisplatin in rectal neuroendocrine carcinoma: a case report

Rectal neuroendocrine carcinomas (NECs) are rare and associated with poorer prognoses compared to conventional adenocarcinomas. The efficacy of adjuvant chemotherapy for resectable rectal NECs remains uncertain. Herein, we present a case of rectal NEC successfully treated with postoperative chemotherapy using irinotecan plus cisplatin. A 48-year-old woman with a history of endometrial cancer presented with an intramural rectal tumour detected on follow-up imaging. Colonoscopy revealed a 30 mm submucosal tumour, and laparoscopic low anterior resection was performed. Histopathological examination showed poorly differentiated atypical cells with solid growth patterns. Metastasis from the uterine cancer was ruled out due to histological differences between the primary uterine tumour and the rectal lesion, as well as the absence of hormone receptor immunohistochemical expression. Further immunohistochemical analysis revealed diffuse CD56 positivity, a high mitotic rate (> 20/10 high power fields) and a Ki-67 labelling index exceeding 70%. Based on these findings, a diagnosis of rectal NEC, T3N0M0, Stage IIB (UICC 8th edition), was established. Given the aggressive nature of the tumour evidenced by a high Ki-67 labelling index, adjuvant chemotherapy comprising six cycles of irinotecan plus cisplatin was administered to mitigate the risk of recurrence. At the 3-year follow-up, the patient was free of disease recurrence. This case highlights the importance of multidisciplinary surgical interventions followed by adjuvant chemotherapy in managing rectal NECs.