inhibiting activity, and otastat potassium, which reduces the gastrointestinal toxicity [1].Derived from phase I data, Japanese early phase II studies of S-1 adopted a fi xed dose of 75 mg twice a day. However, skin rash and diarrhea hindered further conduct of the trial, and the dose was reduced to 50 mg twice a day. In consideration of the safety profi les of the fi xed-dose schedule, the dose of the late phase II trials was modifi ed to 80 mg/m 2 according to the body surface area (BSA). The applied dose ranged from 64 mg/m 2 to 80 mg/m 2 with a graded system; 80 mg for BSA less than 1.25 m 2 , 100 mg for BSA 1.25-1.50 m 2 , and 120 mg for BSA more than 1.5 m 2 . This BSA-based dosing system differed from the Western dosing system in that it fi xed the dosage for patients with a BSA greater than 1.5 m 2 . As a result, in patients with a BSA of more than 1.5 m 2 , the actual administered dose is not 80 mg/m 2 and there is a risk of underdosing. However, the safety profi le using this system is better than with a fi xed dosing schedule, and S-1 with this dosing system has been the preferred oral agent for the treatment of gastric cancer in Japan.Based on the Japanese response evaluation criteria, which include primary gastric cancer as a measurable lesion, S-1 demonstrated excellent activity in patients with advanced gastric cancer, with a response rate of 45%-54% in early phase II Japanese trials [2][3][4]. In these trials, even though the incidence of overall toxicity was as high as 83%, the toxicity profi le was mild, with a less than 10% incidence of grade III or IV toxicities. And in a post-marketing survey, the incidence of toxicity was 74.1% with the 80 mg/m 2 Japanese dosing system with 4-week treatment and a 2-week rest schedule. This incidence of general toxicity was almost equal to that in the pre-marketing clinical trials. The major reasons for discontinuation of S-1 during the fi rst or second cycle of the treatment were disease symptom progression (43%) or toxicities (33%). The adverse reactions during each cycle appeared mainly during the 2-3 weeks after Abstract S-1, a novel oral fl uoropyrimidine, has shown remarkably good tolerability in Korean gastric and colorectal cancer patients due to its favorable safety profi le. Myelosuppression and diarrhea were the events that precluded dose escalation in Japan, whereas gastrointestinal toxicity and skin reaction were the major limiting factors in Western countries. In contrast, the major adverse event in Korean patients was anemia, which appeared early in the S-1 treatment period and varied among patients. Conventional comparative genomic hybridization (CGH) is used to screen for chromosomal copy number variations such as gene gain, loss, amplifi cation, and deletion. This technique can provide information about genetic instability and chromosomal rearrangements. However, the low resolution of 5-10 Mb is a caveat with conventional CGH. cDNA microarray-based CGH is a useful technique for achieving higher resolution for the detection of genomic aberra...