Background: Some phase II and III studies of second-line chemotherapy for metastatic or advanced gastric cancer have been reported in recent years. Irinotecan is one of the standard regimen for second-line therapy. On the other hand, the efficacy of continuing trastuzumab (Tmab) beyond progression in patients (pts) who had previously been treated with Tmab plus standard first line chemotherapy has not been reported. We conducted this study to assess the efficacy and safety of Tmab with irinotecan in HER2-positive gastric cancer pts previously treated with Tmab (UMIN ID: 000007636). Methods: Patients with HER2-positive metastatic or advanced gastric cancer who were previously treated with Tmab and failed were included. Pts received Tmab every 3 weeks and irinotecan every 2 weeks. Primary endpoint was response rate (RR), and secondary endpoints were progression-free survival (PFS), six-month survival rate, safety, sub-group analysis by HER2 status (IHC 3+ group, IHC 2+/FISH positive group), and so on. Results: Only 16 pts were enrolled from 9 institutions in three years during a pre-planned registration period. We stopped this study on the way, unfortunately. In a total of 16 pts, one patient was excluded and 15 were analyzed. Median age was 65, male/female; 9/6, ECOG PS 0/1; 8/7, and IHC 3+/IHC 2+ and FISH positive; 10/5, respectively. Response rate was 7% and disease control rate was 53%. Median PFS and overall survival (OS) were 2.4 (95%C.I.; 0.0-5.2 months) and 9.7 months (95%C.I.; 8.2-11.2 months), respectively. Six-month PFS rate was 13%. In sub-group analysis by HER2 status, median PFS of IHC 3+ and IHC 2+/FISH positive were 2.2 and 2.4 months, respectively. Median OS of each groups were 8.8 and 10.8 months. The most frequently reported grade 3-4 adverse events were neutropenia (40%), anemia (27%), anorexia (33%), and fatigue (33%). Conclusions: This study was closed prematurely due to poor accrual. It seemed that continued use of Tmab and irinotecan beyond disease progression has not significant clinical benefit in HER2-positive metastatic or advanced gastric cancer pts previously treated with Tmab. Clinical trial information: UMIN000007636.