Safety and Efficacy of the S-1/Temozolomide Regimen in Patients with Metastatic Neuroendocrine Tumors.

PURPOSE: Both capecitabine alone and capecitabine in combination with temozolomide have activities against neuroendocrine tumors (NETs). However, the role of S-1 in NETs is still unknown. We performed a study to evaluate the safety and efficacy of the S-1/temozolomide (STEM) regimen in patients with locally advanced or metastatic NETs.

METHODS: A retrospective review was conducted in 20 patients with locally advanced or metastatic NETs treated with the STEM regimen. Of the patients, 15 (75.00%) had failed 1 or more lines of treatment with somatostatin analogues, sunitinib, everolimus, anlotinib, or other chemotherapy regimens. The patients received S-1 at 40 mg/m2 orally twice daily on days 1-14 and temozolomide 200 mg orally once daily on days 10-14 of a 21-day cycle. The patients were followed up for evidence of object response, toxicity, and progression-free survival.

RESULTS: Response to treatment was assessed using RECIST 1.1. Eight patients (40.00%) achieved a partial response (PR), and another 8 (40.00%) had stable disease (SD). The clinical benefit rate (PR and SD) was 80.00%. The median progression-free survival was not achieved. Only 1 patient (5.00%) had grade 3 adverse events. Among the patients with NETs of different origins, 4 (40.00%) and 5 (50.00%) with pancreatic NETs attained PR and SD, respectively. Four (40.00%) and 3 patients (30.00%) with nonpancreatic NETs attained PR and SD, respectively.

CONCLUSIONS: The STEM regimen is exceptionally highly active and well tolerated in patients with locally advanced or metastatic NETs. Even in patients who showed disease progression with previous therapies, it is still highly active. In this 20-patient study, the regimen appeared to be similarly active in pancreatic endocrine tumors and nonpancreatic NETs.