The main reasons for S-1 dose decrease in the 3 patients (7.7%) were grade 3 diarrhea, anorexia, and stomatitis, respectively. The main reasons for dose interruption in the 3 patients (7.7%) were grade 3 vomiting, abdominal pain, and liver enzyme elevation, respectively. The median number of chemotherapy cycles before S-1 dose decrease and interruption was 4 (range 2–6) and 5 (range 2–10), respectively. Course was prolonged by 7 days until the grade 3 liver enzyme elevation decreased to grade 1 in 1 patient. Five patients (12.8%) discontinued treatment before progression not due to AEs, with a median number of treatment cycles as 3 (range 1–6) (supplementary Table S1). Second-line treatment was given to 21 (53.9%) of the 39 patients, among whom 5.1% received palliative surgery while 48.8% received oxaliplatin-based, irinotecan-based, or taxane-based chemotherapy (supplementary Table S2).