Increased response of oxaliplatin or irinotecan on in vitro chemosensitivity to 5-fluorouracil in patients with colorectal cancer

Purpose: Five-fluorouracil (5-FU) is the basement drug of chemotherapy in patients with colorectal cancer. Recently, 5-FU and oxaliplatin or irinotecan is to be used by merging. This study investigated the chemosensitivity of 5-FU in patients with colorectal cancer, the additional effects of oxaliplatin or irinotecan to chemosensitivity when they are combined, and the effects of clinicopathologic factors to chemosensitivity. Methods: We performed in vitro chemosensitivity test for the fresh tumor tissue of 48 patients of colorectal cancer and evaluated the chemosensitivity to standard drugs (5-FU, 5-FU plus oxaliplatin: FOx, and 5-FU plus irinotecan: FIri) by using Histoculture drug response assay. Results: The average chemosensitiviy of FOx and FIri were significantly higher than that of 5-FU (32.3% and 36.0% vs. 21.8%, P<0.001). The chemosensitivity of FOx in the lymph node (LN) negative group was higher than LN positive group (35.3% vs. 19.3%, P=0.008). The group of under 70-year-old and the group of negative distant metastasis showed the trends of increased sensitivity to FOx (P=0.052, respectively). The chemosensitivity to FIri in the well or moderately differentiated group was significantly higher than the poorly differentiated goup (35.2% vs. 15.0%, P=0.038). Ki-67 positive group showed significantly increased chemosensitivity to FIri (P=0.021). Conclusion: This study demonstrates that combination of oxaliplatin or irinotecan to 5-FU can be more effective than 5-FU on in vitro chemosensitivity assay in colorectal cancer tissues. Oxaliplatin might be effective in LN negative group, and irinotecan might be effective in well differentiated group and Ki-67 positive group.