Frequency of EGFR and KRAS Mutations in Japanese Patients with Lung Adenocarcinoma with Features of the Mucinous Subtype of Bronchioloalveolar Carcinoma

IntroductionAdenocarcinoma of the lung, especially bronchioloalveolar carcinoma (BAC) and adenocarcinoma with BAC features (AWBF), is potentially sensitive to epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs); however, the efficacy seems to differ between the histologic subtypes. Mucinous BAC and AWBF (MBAC/AWBF) are not particularly responsive to EGFR-TKIs compared with nonmucinous BAC/AWBF (N-MBAC/AWBF). This may be due to the rarity of EGFR mutations and high frequency of KRAS mutations in MBAC/AWBF in contrast to N-MBAC/AWBF.MethodsOne hundred ninety-one patients with adenocarcinoma of the lung underwent surgery at our institution. There were 59 patients (30%) diagnosed with BAC/AWBF; 20 had MBAC/AWBF (10%) and 39 had N-MBAC/AWBF (20%). We isolated 44 tissue specimens from these patients (20 consecutive cases of MBAC/AWBFs and 24 randomly chosen cases of N-MBAC/AWBFs as the control group), and we analyzed them for EGFR and KRAS mutations. We used the peptide nucleic acid-locked nucleic acid polymerase chain reaction clump method to detect EGFR mutations and conventional DNA sequencing to identify KRAS mutations.ResultsEGFR mutations were found in three of the 20 MBAC/AWBFs (15%) and in 14 of the 24 N-MBAC/AWBFs (58%) (p = 0.005). In addition, there were 14 KRAS mutations identified in the 20 MBAC/AWBFs (70%) and seven in the 24 N-MBAC/AWBFs (29%) (p = 0.0144).ConclusionsThe incidence of EGFR mutation is low and that of KRAS mutation is frequent in MBAC/AWBFs. Conversely, the incidence of EGFR mutation is high and KRAS mutation is low in N-MBAC/AWBFs. Based on these findings, EGFR-TKIs may not be effective in patients with MBAC/AWBF.