[Effects of irinotecan and 5-FU combination therapy in gastric cancer--is combination therapy synergic?].

Unlabelled: The response rate of Irinotecan for gastric cancer is reported to be 18. 4%. The rate is improved by combination with 5-FU. However, it remains unclear whether or not the effect of the two drugs is synergy or antagonistic. The purpose of this study is to clarify whether the effect of Irinotecan and 5-FU in gastric cancer is synergy or antagonistic. We performed study using 13 specimens removed surgically and 2 specimen collected from ascites. We performed the Collagen Gel Droplet Embedded Culture Drug Sensitivity Test (CD-DST) with 3 assumptions. In the first assumption, we let 5-FU come in contact with a tumor at a level of 1 mg/mL for 24 hours. The second assumption was SN-38 at a level of 30 mg/mL for 24 hours and the 3rd assumption was SN-38 at a level of 30 mg/mL and 5-FU at a level of 1 mg/mL for 24 hours. If the combination index was more than 1, the combination therapy was judged as synergic; if less than 1, it was considered antagonistic.

Results: The inhibition rate of combination therapy was significantly higher than that of monotherapy. The inhibition rate of combination therapy was significantly correlate with that of monotherapy (Irinotecan; r=0.704, p=0.003, 5-FU; r=0.746, p=0.001). The combination index was antagonistic in only 6 of 15 cases. However, it was synergic in all well-differentiated adenocarcinomas (4/4).

Discussion: We conclude that combination therapy is antagonistic in most cases of gastric cancer in vitro. However, it may be synergic in well-differentiated adenocarcinomas.