Clonal Origin Evaluated by Trunk and Branching Drivers and Prevalence of Mutations in Multiple Lung Tumor Nodules

Introduction: Differentiation between intrapulmonary metastasis (IPM) and multiple primary lung cancers (MPLC) in patients with synchronous or metachronous lung tumor nodules is critical but challenging. Objective: We proposed an algorithm to evaluate clonal origin based on trunk (initiating) versus branching drivers and the prevalence of mutations in lung adenocarcinomas. Methods: Driver mutations were examined using next-generation sequencing in five trunk driver genes (BRAF, EGFR, ERBB2, KRAS, and NRAS) and three branching driver genes (ATK1, PIK3CA, and TP53). Results: Mutational profiling supported same clonality and likely same clonality, respectively, in 39 and 14 of 66 pairs of specimens with known identical clonal origin. Discordance of TP53 mutations (branching drivers) was observed in three pairs. Subsequent analyses of 30 pairs of synchronous or metachronous lung tumor nodules revealed different clonality and likely different clonality in 17 and 2 pairs, respectively, including three pairs with similar histomorphology; same clonality and likely same clonality in three and five pairs, respectively, including two pairs with different histomorphology; and inconclusive or noninformative results in three pairs. Conclusion: While discordance of trunk drivers indicated MPLC in patients with synchronous or metachronous lung tumor nodules, discordance of branching drivers did not exclude IPM. Concordance of uncommon drivers supported IPM, whereas concordance of common drivers did not exclude MPLC. Additional recommendations from official organizations are needed to guide applications of molecular markers in defining clonality of multiple lung tumor nodules.