Association of genetic polymorphisms in the folate pathway with efficacy and toxicity of methotrexate in pediatric osteosarcoma.

Abstract

10051 Background: Osteosarcoma is the most common childhood malignant bone tumor. Methotrexate (MTX), one of the main drugs used for osteosarcoma, is a representative folic acid antagonist. Genetic polymorphisms in folate pathway genes are expected to influence the response and toxicity of high-dose MTX therapy. However, there are scarce data available regarding associations between genetic polymorphisms and pediatric osteosarcoma. This study evaluated the effect of common genetic polymorphisms in the folate metabolic pathway on overall survival, event-free survival and histological response to neoadjuvant chemotherapy including high-dose MTX. In addition, whether these genetic polymorphisms affect the concentrations of MTX and toxicity after high-dose MTX therapy for osteosarcoma was investigated. Methods: Blood and tissue samples from 48 osteosarcoma patients who had completed chemotherapy were obtained, and the following polymorphisms were analyzed; RFC1 80G>A, DHFR 829C>T, MTHFR 677C>T, MTHFR 1298A>C, AMPD1 34C>T, ATIC 347C>G, and ITPA 94C>A. Associations between candidate polymorphisms and survival, histological response (tumor necrosis rate) and MTX level and toxicity after high-dose MTX therapy were analyzed. Results: Event-free survival significantly decreased in DHFR 829 CC homozygote (P=0.045). Variant carriers of MTHFR 677C>T had tendency towards poor histological response (P=0.078). MTX concentration was significantly associated with RFC1 80G>A polymorphism (P=0.027). Liver toxicity after high-dose MTX was associated with ATIC 347C>G (P=0.043) and tended to increase in carriers of MTHFR 677C>T (P=0.069). Severe stomatitis was associated with RFC1 80G>A (P=0.012). Conclusions: This study has demonstrated that several genetic polymorphisms in folate pathway can significantly influence therapeutic response, clinical outcome and MTX level and toxicity after high-dose MTX therapy in osteosarcoma patients. If these associations are independently validated, these variants could be used as genetic predictors of clinical outcome in the treatment of patients with osteosarcoma, aiding the development of tailored therapeutic approaches.