Multicenter Retrospective Study of Efficacy of Systemic Therapy in Patients with Neuroendocrine Tumor Grade 3 (JOSC-2001).

Background: Neuroendocrine tumor G3 (NET G3) is a new category introduced in the WHO 2017 classification. Accordingly, evidence regarding chemotherapy for NET G3 is limited. A multicenter, retrospective analysis was performed to evaluate the outcomes of systemic therapy for NET G3 and to identify the optimal regimens.

Methods: Patient demographic and treatment outcome data were retrospectively collected for 73 patients with pathologically diagnosed NET G3 who started chemotherapy at participating institutions between January 2011 and December 2019, excluding those who were ineligible by central pathological review. The chemotherapy regimens used and their efficacies were evaluated.

Results: Of the 73 patients, 47 had pancreatic NETs, 10 had gastrointestinal NETs, and 16 had NETs at other sites. Central pathological review was performed for 44 patients, with a concordance rate of 95%. Initial treatment regimens included NET-based treatment (somatostatin analogue, molecular-targeted agent, cytotoxic chemotherapy such as streptozocin and temozolomide) for 37 patients, NEC-based treatment (platinum-containing chemotherapy) for 32 patients, and other regimens for 2 patients. There were no significant differences in progression-free survival (PFS), or overall survival (OS) between patients receiving NET-based and NEC-based treatment, or among the individual treatment regimens. However, the response rate (RR) was higher for NET-based cytotoxic chemotherapy (50%) compared with NEC-based treatment (16%), suggesting greater efficacy of NET-based cytotoxic chemotherapy.

Conclusions: Although no significant difference in PFS or OS was found among the chemotherapy regimens for NET G3, RR was notably higher for NET-based cytotoxic chemotherapy than for NEC-based treatment.