Multicenter, retrospective, observational study of outcomes of treatment for unresectable neuroendocrine tumors G3 of gastroenteropancreatic or unknown primary origin.
Authors: Shibuki Taro , Okuyama Hiroyuki , Okano Naohiro , Mizukami Takuro , Yanagimoto Hiroaki , Ohba Akihiro , Kita Emiri , Kobayashi Noritoshi , Kobayashi Satoshi , Furukawa Takaaki , Asama Hiroyuki , Tsumura Hidetaka , Kamata Ken , Umemoto Kumiko , Suzuki Yuko , Kojima Motohiro , Imaoka Hiroshi , Terashima Takeshi , Ueno Makoto , Ikeda Masafumi 
Published: January 2025

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Background:
The 2017 edition of the WHO classification categorized neuroendocrine neoplasms (NEN) as neuroendocrine tumors (NET) G1, G2, G3, and neuroendocrine carcinoma (NEC). Prior to 2017, NET G3 was categorized as NEC in the WHO 2010 classification. Platinum-based chemotherapy, commonly used as first-line treatment for these tumors, shows suboptimal efficacy for NET G3. Additionally, large-scale studies and robust evidence on chemotherapy outcomes for NET G3 are lacking. We investigated chemotherapy regimens for NET G3 and evaluated their outcomes.
Methods:
We included 73 patients (pts) who were clinically and pathologically diagnosed with unresectable NET G3 of gastroenteropancreatic or unknown primary origin and who started chemotherapy between Jan 2011 and Dec 2019. Clinical data were collected retrospectively and analyzed for regimen selected, treatment efficacy, and prognostic factors. A central pathological review was conducted if tissue samples were available.
Results:
The median age of pts was 65 years (range 27-85 years), with 45 being male. Among the pts, 49 had pancreatic NETs, 10 had gastrointestinal NETs, and 14 had NETs of unknown primary origin. The median Ki-67 index was 30% (range 20-70%). Twenty-seven patients (37%) had received prior treatment, such as surgery or local therapy. A central pathological diagnosis was confirmed NET G3 in 42 out of 44 patients (95%). Primary treatment regimens were NET-based (somatostatin analogues, everolimus, sunitinib, streptozocin-based chemotherapy, and capecitabine and temozolomide [CAPTEM]) and NEC-based (platinum-based chemotherapy) in 54% and 44% of patients, respectively. NET-based regimens were selected in 36% and 78% of pts, respectively, before and after publication of the WHO 2017 classification. The overall response rate (ORR) was 16% for NEC-based regimens and 19% for NET-based regimens. However, when focusing on NET-based chemotherapy (streptozocin-based and CAPTEM), the ORR was 54%. Median progression-free survival (PFS) was 118 days (95% confidence interval [CI]: 60-337 days) for NET-based regimens and 229 days (95%CI: 133-426 days) for NEC-based regimens. Median overall survival (OS) was 841 days for NET-based regimens (95%CI: 480-989 days) and 658 days (95%CI: 455-1144 days) for NEC-based regimens. There were no significant differences in PFS or OS between the regimens. In multivariable analysis, hepatic tumor volume >25% was a negative predictor of PFS, and NSE ≥16.3 ng/mL was a negative predictor of OS.
Conclusions:
Since the introduction of NET G3 in the WHO classification, NET-based regimens have become the preferred treatment choice. Although there were no significant differences in PFS or OS between the regimens, the NEC-based regimens was limited. Pts with high hepatic tumor volume or elevated NSE levels had a worse prognosis.