Background: No standard regimen is yet established for advanced poorly differentiated neuroendocrine carcinoma (PDNEC) although regimens for small-cell lung carcinoma are usually adopted such as irinotecan + cisplatin (IP) or etoposide + cisplatin (EP). Our aim was to respectively investigate outcomes for advanced PDNEC of the digestive system according to patient characteristics and regimens. Methods: Data was collected from patient medical records at 23 hospitals in Japan. The selection criteria were as follows: 1) histologically proven PDNEC, small cell carcinoma, mixed endocrine-exocrine carcinoma with a PDNEC component, or histologically proven neuroendocrine tumor with rapidly progressive clinical course; 2) primary tumor arising from the gastrointestinal tract (GI) or the hepato-biliary-pancreatic system (HBP); and 3) inoperable or recurrent disease treated with systemic chemotherapy (Cx) between April 2000 and March 2011. Results: This study included 258 patients (males/females, 182/76) with median age of 62.5 years. Primary sites were esophagus/stomach/small bowel/colorectum/hepato-biliary system/pancreas in 85/70/6/31/31/35 patients (pts). According to the primary sites, the median overall survival period (mOS) was 13.4/13.3/29.7/7.6/7.9/8.5 months, and that of GI/HBP was 13.0/7.9 months, respectively. Most common regimen was IP (160 pts, 62%), followed by EP (46 pts, 18%). For IP/EP patients, response rates (RR) were 50%/27%, the median progression free survival periods (mPFS) were 5.2/4.0 months. Second line Cx was performed for 88 pts (55%)/28 pts (61%) and mOS from first line Cx were 13.0/7.3 months in IP/EP groups. Multivariate analysis demonstrated that a primary site of HBP (HR=1.96, p=0.003) and performance status of 2 and more (HR=2.32, p=0.01) were independent unfavorable prognostic factors of PDNEC patients treated with systemic Cx, while the hazard ratio comparing IP with EP was 0.79 (p=0.305). Conclusions: PDNEC of HBP had poorer prognosis than GI. IP was the most common treatment regimen and seemed to show better treatment outcomes than EP.