KRAS Analysis for EGFR-Directed Therapy in Colorectal Cancer (CRC): A Review of Greater Than 2500 Cases Using an Allele-Specific Assay for Detection of 12 Mutations
B Horten, DA Sirko-Osadsa, M Da Silva, M Dugan, C Chenet-Monte, BA Allitto. Genzyme Genetics, New York, NY; Genzyme Genetics, Westborough, MA; Genzyme Genetics, Los Angeles, CA
Background: EGFR promotes tumor growth in part through KRAS stimulation. Inhibition of EGFR is a frequent therapy in CRC. However, when KRAS undergoes mutation, KRAS drives tumor growth independent of EGFR and EGFR-directed therapy. To exclude ineffective EGFR-directed CRC therapy, KRAS mutation analysis has recently emerged as a significant CRC biomarker. The purpose of this study is to review KRAS mutation results of CRC samples received for testing in our laboratory.
Design: KRAS mutation analysis was performed on tumors from 2583 colorectal cancer patients. Biopsy material was enriched for tumor using manual microdissection. The extracted DNA was quantified and amplified by polymerase chain reaction (PCR) using primers to exon 2 of the KRAS gene. PCR products were subjected to single nucleotide extension to detect mutation at codons 12 and 13; primer extension products were analyzed by capillary electrophoresis.
Results: Eleven of 12 possible mutations in codons 12 and 13 were detected. The overall mutation detection rate was 40%. 78% of the mutations were present in codon 12 with the remaining 22% in codon 13. Within codon 13, the vast majority of mutations (93%) were G13D , with 5% G13C, 1% G13V, and 1% G13R. The latter 3 mutations are rarely examined in most current KRAS analyses.
Conclusions: The detection rate for KRAS mutations in CRC samples tested in our laboratory is consistent with published data. Most laboratories currently performing KRAS testing examine only 7 mutations. In our laboratory 11/12 mutations in codons 12 and 13 were detected. While the frequency of some of these mutations is low, a test that maximizes the detection rate is needed since critical therapeutic decisions are made based on KRAS mutation status.
Tuesday, March 10, 2009 11:15 AM
Platform Session: Section C, Tuesday Morning