KRAS mutations (MTs) in non-small cell lung cancer (NSCLC) versus colorectal cancer (CRC): Implications for cetuximab therapy.

Abstract

10529 Background: KRAS MTs have been associated with a diversity of biologic functions, and have both prognostic and predictive consequences in NSCLC and CRC. Little data exist comparing the specifics of KRAS MTs in the two cancers. In CRC, benefit from the cetuximab is mainly limited to patients whose tumors are KRAS wild-type (WT). However, recent studies show no such predictive value in NSCLC. We hypothesized that the unique molecular biology and tobacco carcinogen-related etiology of NSCLC contribute to a divergence in KRAS MT type and EGFR-related dependency. Here, we compare KRAS and EGFR status in NSCLC versus (vs) CRC in the large Response Genetics (RGI) database. Methods: KRAS MTs were assessed in 2,693 specimens (838 CRC and 1165 NSCLC) using DNA from microdissected formalin fixed paraffin embedded tumor specimens. EGFR MTs were determined in 649 NSCLCs. A PCR approach with direct sequencing was used to detect 7 different base substitutions in KRAS and 28 EGFR MTs. Statistics: Fisher's Exact Test. Results: KRAS MTs were found in 39% of CRC and 23% of NSCLC specimens (p < 0.001). EGFR MTs were identified in 16% of NSCLCs. In 447 specimens with both assays, EGFR and KRAS MTs were largely exclusive; 4 specimens harbored both (p < 0.001). The ratio of base transversions to transitions was 3.27 in NSCLC versus 0.77 in CRC (p < 0.001). With regard to histology, in NSCLC KRAS MTs were observed in 28.7% (186/649) of adenocarcinomas vs 3.5% (7/198) of squamous cell carcinomas (p < 0.001). Tobacco carcinogenesis-associated G>T transversions (codon 12 GGT>TGT plus GGT>GTT) comprised 61% of KRAS MTs in NSCLC vs 39% in CRC (p < 0.001). The GGT>GAT transition was most prevalent in CRC at 33.3%. Conclusions: This analysis of the RGI database demonstrates differences between NSCLC vs CRC in both incidence and type of KRAS MTs. Increased frequencies of DNA KRAS transversions were seen in NSCLC, likely linked to tobacco exposure. Distinct MT patterns and biologic function may contribute to differences in predictive value for cetuximab therapy between NSCLC and CRC. Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Response Genetics Amgen, AstraZeneca, Biodesix, Boehringer Ingelheim, Bristol-Myers Squibb, Genentech, Genoptix, GlaxoSmithKline, Lilly, Merck, Novartis, Pfizer, Response Genetics, sanofi-aventis Response Genetics DxS, Response Genetics Abbott Laboratories, Bristol-Myers Squibb, Genentech, Lilly, Merck, Novartis, OSI, Pfizer