Tumor cell sensitivity to standard drugs at their maximum concentrations used ex vivo. These concentrations were: 5-FU and irinotecan 1000 μM; oxaliplatin and mitomycin C 100 μM. Cell survival is expressed as survival index (SI %) in tumor samples from colorectal and gastric cancer. Results are presented as mean values + SE. Number of samples investigated was 15 or 16 for gastric cancer and 51 or 52 for colorectal cancer.