The chemosensitivity of 20 human neoplastic tissues including 13 gastric and 7 colorectal cancers was tested using 5-fluorouracil (5-FU) and its analogues: 1-(2-tetrahydrofuryl)-5-FU (FT), uracil/FT (UFT) and l-hexylcarbamoyl-5-FU (HCFU), and the in vivo subrenal capsule (SRC) assay. The relative variation of tumor size (ΔTS/TS0) was calculated as follows: ΔTS/TS0 = (TS6 -TS0/TS0) x 100%, where TS6 was the tumor size on day 6 and TS0 on day 0, and the chemosensitivity was considered to be sensitive when ΔTS TS0 in the treated group was decreased to below -10%. The mean tumor size was -10.9 ± (SD)10.9% for 5-FU, -12.3± 17.1% for FT, -18.4± 15.8% for UFT and -17.9±15.4% for HCFU. The decrease of tumor size was marked when exposed to UFT (p < 0.01) or HCFU (p<0.02), compared with that to 5-FU. Positive correlations were noted between the tumor sizes of 5-FU and its analogues (5-FU vs. FT, r = 0.851; 5-FU vs. UFT, r = 0.746; 5-FU vs. HCFU, r = 0.685). In 9 tissues resistant to 5-FU, 2 (22%) were sensitive to FT, 4 (44%) to UFT, 5 (56%) to HCFU and 7 tissues (78%) to at least one of these analogues. These results suggest that the SRC assay is useful for predicting the effective drug among 5-FU and 5-FU analogues, for individual patients with cancer.
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