Favorable response of colonic mixed adenoneuroendocrine carcinoma to streptozocin monotherapy

Mixed adenoneuroendocrine carcinoma (MANEC) of the colon is rare and has a poor prognosis. Here, we report a case of MANEC in the ascending colon, in which streptozocin monotherapy achieved a partial response. A 36-year-old woman underwent right hemicolectomy for colonic polyposis, which included ascending colon cancer. Pathological examination revealed that some mucosal polyps were adenocarcinoma while one submucosal polyp was neuroendocrine carcinoma. Adjuvant chemotherapy was not administered, and 5 months after the operation, multiple liver metastases were identified. She was started on modified (5-FU, leucovorin, oxaliplatin) followed by XELOX (capecitabine, oxaliplatin) plus bevacizumab. Although these regimens helped achieve stable disease, computed tomography showed that the hepatic metastatic lesions had enlarged 4 months later. Subsequently, the regimen was changed to streptozocin monotherapy (1000 mg/m², weekly). After 5 cycles, the regimen achieved partial response and was continued for a total of 17 courses without significant adverse events until progressive disease. As a third-line chemotherapy regimen, cisplatin plus etoposide (EP) was administered. The EP regimen reduced the size of the hepatic and ovarian metastatic lesions but severe neutropenia and anemia was observed. Amrubicin monotherapy was also administered as fourth-line chemotherapy but a good clinical response was not detected, and the patient died 20 months after the operation. Streptozocin monotherapy has the potential to be a therapeutic option for mixed adenoneuroendocrine carcinoma of the colon.