Detection and Clinical Significance of Intratumoral EGFR Mutational Heterogeneity in Chinese Patients with Advanced Non-Small Cell Lung Cancer

PURPOSE This study evaluated occurrence and potential clinical significance of intratumoral EGFR mutational heterogeneity in Chinese patients with non-small cell lung cancer (NSCLC). MATERIALS AND METHODS Eighty-five stage IIIa-IV NSCLC patients who had undergone palliative surgical resection were included in this study. Of these, 45 patients carried EGFR mutations (group-M) and 40 patients were wild-type (group-W). Each tumor sample was microdissected to yield 28-34 tumor foci and Intratumoral EGFR mutation were determined using Denaturing High Performance Liquid Chromatography (DHPLC) and Amplification Refractory Mutation System (ARMS). EGFR copy numbers were measured using fluorescence in situ hybridization (FISH). RESULTS Microdissection yielded 1,431 tumor foci from EGFR mutant patients (group-M) and 1,238 foci from wild-type patients (group-W). The EGFR mutant frequencies in group-M were 80.6% (1,154/1,431) and 87.1% (1,247/1,431) using DHPLC and ARMS, respectively. A combination of EGFR-mutated and wild-type cells was detected in 32.9% (28/85) of samples by DHPLC and 28.2% (24/85) by ARMS, supporting the occurrence of intratumoral heterogeneity. Thirty-one patients (36.5%) were identified as EGFR FISH-positive. Patients harboring intratumoral mutational heterogeneity possessed lower EGFR copy numbers than those tumors contained mutant cells alone (16.7% vs. 71.0%, P<0.05). Among 26 patients who had received EGFR-TKIs, the mean EGFR mutation content was higher in patients showing partial response (86.1%) or stable disease (48.7%) compared with patients experiencing progressive disease (6.0%) (P = 0.001). There also showed relationship between progression-free survival (PFS) and different content of EGFR mutation groups (pure wild type EGFR, EGFR mutation with heterogeneity and pure mutated EGFR) (P = 0.001). CONCLUSION Approximately 30% of patients presented intratumoral EGFR mutational heterogeneity, accompanying with relatively low EGFR copy number. EGFR mutant content was correlated with the response and prognosis of EGFR-TKIs.