Immunohistochemical analysis of organic anion transporter 2 and reduced folate carrier 1 in colorectal cancer: Significance as a predictor of response to oral uracil/ftorafur plus leucovorin chemotherapy

Colorectal cancer is one of the most common malignancies in developed countries and chemotherapy is the standard treatment option for advanced colorectal cancer. Identification of biomarkers for predicting response to uracil/ftorafur plus leucovorin (UFT/LV) chemotherapy is an important issue in colorectal cancer treatment. Organic anion transporter 2 (OAT2) and reduced folate carrier 1 (RFC1) are the major uptake transporters of 5-fluorouracil (5-FU) and LV, respectively. In the present study, the correlation between OAT2 and RFC1 expression and histological response to preoperative UFT-based (UFT or UFT/LV) chemotherapy was investigated. Pre-treatment biopsy specimens obtained from 45 patients were evaluated for OAT2 and RFC1 expression levels by using an immunohistochemical approach. A high expression of OAT2 and RFC1 was significantly correlated with good response to UFT-based chemotherapy (P<0.0001 and P= 0.002, respectively). In multivariate logistic regression analysis, a high OAT2 expression was an independent predictor of good response to UFT-based chemotherapy (P=0.02), unlike RFC1 expression. High expression levels of OAT2 were significantly correlated with a good response in the UFT-treated (P= 0.04) as well as the UFT/LV-treated (P<0.0005) groups; however, RFC1 expression levels were significantly correlated with a good response only in the UFT/LV-treated group (P=0.02). Therefore, immunohistochemical analysis of OAT2 and RFC1 may serve as a useful tool for predicting the efficacy of UFT/LV treatment regimens in colorectal cancer patients.