13160 Background: First-line therapy for metastatic colorectal cancer (CRC) is 5-fluorouracil/leucovorin in combination with oxaliplatin (ie, FOLFOX™) or irinotecan (ie, FOLFIRI). Optimizing this therapy for an individual patient, however, is complicated due to wide variability in drug response and potential for toxicity. Such variability may be due to functional genomic polymorphisms in the drug target gene or in the metabolizing or DNA repair enzyme genes. We report, herein, development and validation of 2 new assays that, together, detect 7 polymorphisms associated with CRC drug response and toxicity. Methods: The first assay (SNaPshot) simultaneously detects 4 polymorphisms by using primers targeting the ERCC1, XPD, GST-P1, and XRCC-1 genes, single nucleotide primer extension of PCR products, electrophoresis and fluorescent detection on an ABI PRISM® 3100 Genetic Analyzer, and data analysis using GeneMapper® software (Applied Biosystems, Inc.). The second assay (F-PCR) simultaneously detects 3 polymorphisms using paired primers targeting the TS and UGT1A1 genes. One primer per pair is labeled with a fluorescent tag, and electrophoresis, detection, and data analysis are performed as described for the SNaPshot assay. Results: Based on fragment size and color, the intra- and interassay precision for SnaPshot ranged from 0.04%-0.51% and 0.14%-0.59%, respectively, and for F-PCR from 0.02%-0.16% and 0.09%-0.29%, respectively. There was 100% concordance in the genotypes determined in 3 separate SNaPshot (n=44 samples) and F-PCR (n=32 samples) assays. Furthermore, there was 100% agreement between genotypes determined by the SNaPshot method and those determined by RFLP (n=10) and between genotypes determined by the F-PCR method and those determined by pyrosequencing (n=17). Conclusions: Our multiplex SNaPshot and F-PCR methods can accurately detect 7 polymorphisms associated with CRC drug response and toxicity. These multiplex PCRs should lead to improved precision and ease of interpretation relative to that of single PCR methods. These methods may help the clinician optimize CRC therapy for individual patients. No significant financial relationships to disclose.