Phase II study of temozolomide monotherapy in patients with extrapulmonary poorly differentiated neuroendocrine carcinoma that were resistant to platinum-based chemotherapy

Abstract Background: Extrapulmonary poorly differentiated neuroendocrine carcinoma (EPNEC) is a lethal disease with a poor prognosis. Platinum-based chemotherapy is used as the standard first-line treatment for unresectable EPNEC. Several retrospective studies have reported the results of the utilization of temozolomide (TMZ) as a drug for the second-line treatment for EPNEC. Methods:Patients with unresectable EPNEC that were resistant to platinum-based combination chemotherapy were recruited for a prospective phase II study of TMZ monotherapy. A 200 mg/m2 dose of TMZ was administered from day 1 to day 5, every four weeks. Response rate (RR) was evaluated as the primary endpoint. The presence of O6-methylguanine DNA methyltransferase (MGMT) in EPNEC patients was also evaluated as exploratory research. Results: Thirteen patients were enrolled in this study. Primary lesions were pancreas (n=3), stomach (n=3), duodenum (n=1), colon (n=1), gallbladder (n=1), liver (n=1), uterus (n=1), bladder (n=1), and primary unknown (n=1). Each case was defined as pathological poorly differentiated neuroendocrine carcinoma from surgical resected and/or biopsied specimens. The median Ki67 labeling index was 60% (range: 22%-90%). The RR was 15.4%, progression free survival was 1.8 months (95% confidence interval [CI], 1.0-2.7), overall survival (OS) was 7.8 months (95% CI, 6.0-9.5), and OS from first-line treatment was 19.2 months (95% CI, 15.1-23.3). No grade 3 or 4 hematological toxicity had occurred and grade 3 nausea and appetite loss had occurred one case. One case presented MGMT deficiency and this case showed partial response. Conclusion: TMZ monotherapy is a feasible, modestly effective, and safety treatment for patients with unresectable EPNEC following platinum-based chemotherapy. MGMT deficiency may be a reliable biomarker for the response of unresectable EPNEC to TMZ. Trial registration: Registered at April 20, 2013. Registry number: UMIN000010549.