EGFR L858M/L861Q cis Mutations Confer Selective Sensitivity to Afatinib.

Introduction: Tyrosine kinase inhibitors (TKIs) have been developed to treat patients with EGFR-mutant lung cancers. However, the therapeutic efficacy of TKIs in patients with uncommon EGFR mutations remains unclear.

Methods: Next-generation sequencing was performed on a patient's lung adenocarcinoma tumor sample, revealing rare combined in cis (on the same allele) EGFR mutations. Stable Ba/F3 and NIH-3T3 cell lines harboring the mutations were established to investigate the effect of first-, second-, and third-generation EGFR TKIs on cell proliferation by MTS assay and EGFR phosphorylation by Western blotting.

Results: EGFR L858M/L861Q mutations in cis were detected in the tumor of a patient with NSCLC. The patient demonstrated primary resistance to erlotinib and was subsequently treated with afatinib, which caused tumor regression. In in vitro studies, first- and third-generation TKIs exhibited a decreased capacity to prevent EGFR phosphorylation and inhibit cell proliferation in EGFR L858M/L861Q cells compared with cells harboring the common EGFR L858R point mutation. In contrast, afatinib treatment reduced proliferation and inhibited EGFR phosphorylation in L858M/L861Q- and L858R-mutant cells at similar concentrations.

Conclusions: Afatinib may be a beneficial therapeutic option for a subset of patients with lung cancer who harbor rare EGFR mutations in their tumors. Understanding how uncommon mutations affect protein structure and TKI binding will be important for identifying effective targeted therapies for these patients.