Abstract PR2: The genetic status of the EGFR, K-ras, and EML4-ALK genes in multiple primary noninvasive lung adenocarcinomas

Abstract

Abstract Backgrounds: The development of high-resolution CT (HRCT) has enabled the detection of small-sized lung tumors and sometimes multiple tumors. In resected specimens, preinvasive lesions proposed as adenocarcinoma in situ (IASLC/ATS/ERS 2011) are often observed, and these lesions are recognized as primary lung cancer. Formerly, these lesions were classified as non-mucinous bronchioloalveolar carcinoma (BAC), of which non-invasive tumors were classified as Noguchi's type A or B. The mutations of EGFR, K-ras and ALK are defined as so-called driver mutations, which drive tumor formation and maintenance. We analyzed the genotype of the EGFR and K-ras genes, and the expression of EML4-ALK fusion gene in synchronous multiple non-invasive adenocarcinomas, to evaluate the possibility of multicentric carcinogenesis. Patients and Methods: There were 9 patients with synchronous multiple adenocarcinomas, 20 mm in diameter or less, who underwent surgery from March 2005 to July 2009. In total, 26 lesions were diagnosed as non-invasive adenocarcinoma. In these 9 patients, 2 tumors were detected in 5 cases, 3 tumors in 2 cases, and 5 tumors in 2 cases. A PCR-based fragment analysis was used as a screening method to detect, and direct sequencing was used to confirm the presence of EGFR (exon 19, 21) and K-ras mutations in macro-dissected materials from paraffin-embedded sections. The expression of EML4-ALK fusion gene was examined by an immunohistochemical analysis. Results: Seventeen of the 26 tumors (65%) had an EGFR or K-ras mutation, and nine tumors had wild type. In the EGFR gene, an exon 19 deletion (▵E746-A750) was detected in 11 tumors, and an exon 21 L858R mutation was detected in 4 tumors. A K-ras codon 12 mutation (G12D) was detected in 2 tumors. Two patients had the same EGFR 19 deletion in all of their tumors, and one had the same K-ras codon 12 mutation in all of their tumors. In one patient, 2 of their 3 tumors had the same EGFR 19 del mutation. In another patient with 5 tumors, 2 tumors had the L858R mutation, 2 had a different type of 19 del mutation, and one showed wild-type of EGFR. In one patient, one tumor showed a 19 del mutation and the other showed a L858R mutation. In 3 cases, same mutation was not detected in their tumors. Therefore, 5 of 9 cases (56%) had the same type of mutation in their multiple tumors. The expression of EML4-ALK, as determined by immunohistochemistry, was not detected in any of the tumors. Conclusion: The EGFR and K-ras genes, which are mutually exclusive, can be used to define clinically relevant molecular subsets of lung adenocarcinoma, and can also define tumor clonality. In several patients in this study, multiple tumors which were defined as pathologically non-invasive tumors, showed the same genetic mutation. These findings demonstrate that multicentric carcinogenesis under the same genetic backgrounds occurs in lung adenocarcinoma. This abstract is also presented as Poster A40.