EGFR mutations are prevalent and independent from K-RAS mutations in lung adenocarcinomas from non-smokers

Abstract

Lung cancer is common in Hong Kong with an unusually high incidence in female non-smokers (NS). Lung cancers in NS are likely to involve different carcinogenic processes from those in smokers, but the molecular targets are unclear. Epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that plays a crucial role in cell proliferation, survival and differentiation. It has been observed that non-small cell lung cancer (NSCLC) patients showing improved clinical response to tyrosine kinase inhibitor (TKI) treatment harbour somatic mutations in EGFR tyrosine kinase domain. Activating point mutations in the RAS oncogene has been recognized in adenocarcinomas of different organs including the lung. In order to find out the prevalence and patterns of EGFR and RAS mutations, as well as their relation with clinicopathological profiles of primary NSCLC in Hong Kong, 228 surgically resected primary lung cancers were analyzed. The tumors included 205 adenocarcinomas (AD), 14 squamous cell carcinomas (SCC) and 9 lymphoepithelioma-like carcinomas (LELC) from 97 men (55 current smokers (SM), 17 NS, 24 ex-smokers (EX) and 1 passive smokers (PS)), and 131 women (7 SM, 92 NS, 13 EX and 19 PS) were studied. PCR amplified products spanning the EGFR mutation hot spots (exons 18-21) were sequenced. An overall mutation rate of 49.1% (112/228) was observed, including 52 in-frame deletions, 5 in-frame insertions and 55 amino acid substitutions. Statistically significant associations were found between EGFR mutations and a) NS (79/109) compared with patients with any level of current or previous tobacco exposure (33/119 SM, PS, EX) or with SM only (12/62), P<0.0001 for both, b) female (83/131) compared to male (29/97), P<0.0001 and c) AD (112/205) compared to non-AD (0/23), P<0.0001. No association was found with patients’ age and pathological tumor stage. The findings suggest that EGFR mutation mediates important non-tobacco induced carcinogenic pathways in AD from NS, in contrast to SCC that are prevalent in smokers or the Epstein Barr virus-related LELC. The frequency of K-RAS codon 12 mutations was analyzed by dot-blot and sequencing which demonstrated 18/228 (7.9%) mutations. The mutations were significantly associated with history of any tobacco exposure (15/119, P=0.006) or SM only (10/62, P=0.002). Furthermore, all the K-RAS mutants were found in tumours with wild type EGFR (P<0.0001). In conclusion, EGFR mutations are prevalent and independent from K-RAS mutations in the carcinogenic process in NS with AD. EGFR mutation status of these patients is useful for predicting potential response to TKI therapy. (Supported by HKSAR RGC grants 7310/01M, 7486/03M, 7468/04M)