537P - Differences in Kras and Braf Mutation Prevalence in Metastatic Colorectal Carcinoma Using High-Sensitivity Taqmelt vs Arms-Scorpion Pcr Assays

Abstract

ABSTRACT Background Activating KRAS mutations are present in approximately 35-40% of patients with metastatic colorectal cancer (mCRC) and have been significantly associated with lack of response to anti-EGFR antibody therapies. Although current guidelines recommend testing for frequent KRAS codons 12/13 mutations (G12D, G12A, G12V, G12S, G12R, G12C and G13D), emerging data indicate that additional KRAS and BRAF mutations might be also predictive of non-responsiveness to anti-EGFR treatment. The present study is aimed to analyze the prevalence of Iow-frequent KRAS and BRAF V600 mutations in caucasian mCRC population. Methods A two institution retrospective cohort of 1238 consecutive KRAS wild type mCRC patients previously studied for frequent 7 mutations in codons 12/13 by the CE-IVD marked ARMS-scorpion real-time polymerase chain reaction PCR (Therascreen, Qiagen) was assayed by the diagnostic TaqMelt PCR assay cobas KRAS Mutation and cobas BRAF V600 Mutation Tests (Roche), which are designed to detect 19 mutations in KRAS codons 12, 13 and 61 (including G12F, G13C, G13R, G13S, G13A, G13V, G131, Q61H, Q61K, Q61R, Q61L, Q61E and Q61P) and BRAF V600 (V600E, V600K and V600D) mutations. DNA was obtained by cobas DNA preparation kit from one single 5um formalin-fixed paraffin-embedded tissue section. Discrepances in data are planned to confirm by next-generation sequencing. Results In all samples, sufficient DNA was obtained for KRAS and BRAF mutational studies. Among 1238 KRAS codons 12/13 wild-type patients by ARMS-scorpion PCR, 166 (13.4%) showed KRAS mutations, 117 (9.5%) in codons 12/13, and 49 (4%) in codon 61. BRAF V600 mutations were detected in 9% cases. In ARMS-scorpion PCR KRAS mutated patients, mutations were confirmed by cobas in all cases. Conclusions The cobas Mutation Tests are robust and reproducible assays that, 1) requires a very small amount of tissue; 2) detects up to 13.4% mutations in codons 12, 13 and 61 of the KRAS gene in wild-type mCRC population; and, 3) 9% of patients showed BRAF mutations in same population. Disclosure All authors have declared no conflicts of interest.