EGFR fluorescence in situ hybridization-positive lung adenocarcinoma: incidence of coexisting KRAS and BRAF mutations

Abstract

Despite growing evidence that epidermal growth factor receptor (EGFR) and v-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS) mutation analysis is the most reliable predictor of the lung carcinoma response to EGFR-targeted therapies, there is still discussion about the role of EGFR fluorescence in situ hybridization (FISH). Studies focusing on EGFR FISH as a predictor of response to EGFR-targeted therapies mostly focused on the relationship between EGFR FISH and EGFR mutations. The incidence of KRAS and V-raf murine sarcoma viral oncogene homolog B1 (BRAF) mutations in EGFR-amplified or EGFR FISH-positive lung adenocarcinomas remains unknown. The aim of this study was to prospectively characterize the incidence of KRAS and BRAF mutations in EGFR FISH-positive surgically treated lung adenocarcinomas. Of 386 primary lung adenocarcinomas, 77 (20%) were EGFR FISH positive by University of Colorado criteria. The incidence of KRAS mutations in EGFR FISH-positive lung adenocarcinomas was 23% and was not significantly different from the incidence of KRAS mutations in EGFR FISH-negative subsets of adenocarcinoma (32%). A higher mean ratio between EGFR and chromosome 7 enumeration probe (EGFR/CEP7) was observed in EGFR-mutated tumors when compared to cases with KRAS mutation (13 versus 4.5, respectively). Our results showed significant number of EGFR FISH positive/amplified lung adenocarcinomas harboring KRAS mutation. It appears that an increase in EGFR/CEP7 ratio to cutoff point of 4.5 may distinguish between coexisting EGFR (FISH ratio of >5) or KRAS (FISH ratio of 2 to 5) mutations. Observations presented here indicate that the patient selection for EGFR-targeted therapies should include EGFR and KRAS mutational analysis, probably complemented by EGFR FISH studies.