Does EGFR mutation define the histological predominant subtype of lung adenocarcinoma?

Abstract

7557 Background: In 2011, invasive adenocarcinomas were newly classified into the five predominant subtypes by IASLC/ATS/ERS: lepidic, papillary, acinar, micropapillary, and solid. The purpose of this study is to investigate the correlation between EGFRmutation and the histological predominant subtype of lung adenocarcinoma. Methods: Among a total of 1,736 patients with lung adenocarcinoma who underwent surgical resection from 2002 to 2011 in National Cancer Center Hospital East, 1,507 were classified into invasive adenocarcinoma. 526 of whom were examined EGFR mutation status. Histological predominant subtypes were evaluated at the maximum cut surface of tumors. The EGFR mutation analysis was performed by PCR-invader method. Treatment efficacy of EGFR-tyrosine kinase inhibitors (TKIs) in 73 relapsed patients with EGFRmajor mutations were also examined. Results: 526 adenocarcinomas were consisted of 95 lepidic (18%), 221 papillary (42%), 80 acinar (15%), 9 micropapillary (2%), and 121 solid predominant subtype (23%). EGFR mutations were detected in 227 adenocarcinomas (43%), and its frequency in the solid subtype (22%) was significantly less than that of other histological subtypes (lepidic 47%, papillary 53%, and acinar 44%; P < 0.01). The proportion of minor mutations, other than exon 21 L858R and exon 19 deletions, were significantly higher in the solid subtype (22%) than that of the others (lepidic 4%, and papillary 12%; P < 0.01). In 73 patients with EGFR major mutations treated by EGFR-TKIs, the response rate was not different between histological subtypes (lepidic 86%, papillary 76%, acinar 89%, and solid 60%). Conclusions: The correlation between histological predominant subtypes of lung adenocarcinoma and the presence of EGFR mutations or the efficacy of EGFR-TKI were not identified in this study. Little is known about the reason why EGFR minor mutations were highly detected in the solid subtype of adenocarcinoma, however it is possibly due to the high frequency of heavy smokers in solid subtype (heavy smoker: solid 67% vs. others 27-44%).