Background: Gemcitabine is one of the standard chemotherapeutic agents for pancreatic cancer. Pancreatic cancer is often associated with cachexia. It had been reported that eicosapentaenoic acid (EPA) reduces proinflammatory cytokines, leading to improvement of cachexia. This study aimed to evaluate the efficacy and safety of gemcitabine with an EPA-enriched oral supplement in patients with unresectable pancreatic cancer. Methods: This phase II study consisted of patients (pts) who were randomly categorized into Arm A (1000 mg/m² gemcitabine was administered on days 1, 8, and 15, every 4 weeks while an EPA-enriched oral supplement (Prosure, EPA 1056mg per pack) was taken daily at the maximum of 2 packs) or Arm B (gemcitabine monotherapy) at a 2:1 ratio. The primary endpoint was the evaluation of the 1-year survival. The sample size of 66 pts was chosen based on the randomized phase II selection design by Simon et al. (1985). The design suggests a correct selection probability of 80% if 1-year survival probabilities are 35% and 25% for two treatment arms. Results: From May 2010 to Oct. 2011, randomized 66 pts were examined (Arm A: 43, B: 23). The 1-year survival probability of Arm A was 35% while Arm B was 19%. The median survival times were 8.2 and 9.7 months, respectively. The hazard ratio was 0.79 [95%CI 0.46-1.37]; (p=0.40). The toxicities were mild and insignificant in both arms. Grade 3/4 toxicities (A/B %) included: neutropenia, 20.9/13.0; leukocytopenia, 30.2/21.7; hemoglobin, 14.0/8.7; thrombocytopenia, 9.3/8.7; nausea, 11.6/0.0; and diarrhea, 0/4.3. Although survival curve did not show significant differences, delayed effect was observed in Arm A. According to subgroup analyses, more beneficial effects were observed in men and pancreatic body-tail patients who took a lot of supplements (Table). Conclusions: Gemcitabine with an EPA-enriched oral supplement in advanced pancreatic cancer may be effective, and further phase III trial is needed. Clinical trial information: UMIN000003658.