Tumor clonal status predicts clinical outcomes of lung adenocarcinoma with EGFR-TKI sensitizing mutation.

Objectives: Intratumoral heterogeneity is one of major causes of resistance to therapeutic. Here, we evaluated clonal status, which may reflect intratumoral heterogeneity, in lung adenocarcinoma with EGFR-TKI sensitizing mutation (mEGFR) and its clinical implications. Materials and Methods: Customized panel comprised of 71 solid tumor-associated genes were applied to the 77 surgically resected lung adenocarcinoma having mEGFR with curative aim. For comparison, whole exome sequencing (WES) data of 45 TCGA-LUAD with mEGFR were extracted from the GDC dataportal. Clonal status was estimated from the allele frequency of the mutated genes using the Maftools package. Results: In the study cohort, the number of mutations per case detected by customized panel was 5 [4-8], and the number of total mutations or subtypes of mutations was not related clinical parameters, including size of tumor and pStage. The number of subclones showed positive correlation with the maximum diameter of primary tumor (Spearman's rho=0.273, P-value = 0.026). Disease-free survival (DFS) was significantly shorter among cases wherein tumors comprised two or more subclones than the cases in which tumors were comprised of one clone (P-value = 0.006, Log-rank test), and multivariate analysis indicated that the number of subclones was an independent determinant of DFS. In the WES of TCGA-LUAD mEGFR, the characteristics of the mutations did not show significant relationship with clinical parameters whereas the cases with clones with two or more showed poorer overall survival than those with one clone (P-value = 0.038, Log-rank test). Conclusions: Number of subclones comprising the primary lesion was positively correlated with tumor size, and was an independent factor affecting clinical outcome, showing that a description of tumor clonality may be helpful for understanding of disease status.