PurposeThe purpose of our study was to evaluate the efficacy of a new combination antiemetic therapy consisting of palonosetron, aprepitant, and dexamethasone in gastric cancer patients undergoing chemotherapy with S-1 plus cisplatin.MethodsThis prospective, multi-institutional observational study assessed patient-reported nausea, vomiting, use of rescue therapy, change of dietary intake, and Functional Living Index-Emesis (FLIE) questionnaire results. The percentages of patients showing complete response (CR; no emesis and non-use of any rescue antiemetics) and complete protection (CP; no significant nausea and non-use of any rescue antiemetics), change of dietary intake, and impact of chemotherapy-induced nausea and vomiting on daily life during the overall (0–120 h after cisplatin administration), acute (0–24 h), and delayed (24–120 h) phases were examined. These findings were compared with our previous study, which used granisetron, aprepitant, and dexamethasone, to assess the relative effectiveness of palonosetron versus granisetron in combination antiemetic therapy.ResultsOf the 72 included patients, 66 (91.6 %), 70 (97.2 %), and 50 (69.1 %) achieved CR, and 48 (66.7 %), 61 (84.7 %) and 49 (68.1 %) achieved CP during in the overall, acute, and delayed phases of cisplatin administration, respectively. Approximately half of the patients had some degree of anorexia. FLIE results indicated that 78.6 % of patients maintained their quality of life. Palonosetron was not superior to granisetron in combination antiemetic therapy.ConclusionsThree-drug combination antiemetic therapy with palonosetron, aprepitant, and dexamethasone was tolerable in gastric cancer patients undergoing treatment with S-1 plus cisplatin. The predominance of palonosetron to granisetron was not demonstrated in this study.