Intrapatient Molecular and Histologic Heterogeneity After First-generation or Second-generation TKI Therapy of NSCLC Patients: Potential Clinical Impact on Subsequent third-generation TKI Treatment

Objectives: The discovery of tyrosine kinase inhibitors (TKI) has remarkably improved the clinical course of patients with non-small cell lung cancer driven by Epidermal Growth Factor Receptor (EGFR) mutations. However, virtually in all cases, the disease resurfaces in a TKI-resistant form that is mainly linked to an acquired EGFR-T790M mutation, a MET amplification, or small cell lung cancer (SCLC) transformation. Third-generation TKIs are able to block tumor growth through an irreversible binding to the T790M-mutated receptor. Such new treatments require the diagnostic analysis of new pathologic tissue or a liquid biopsy to detect the presence of the T790M mutation. Materials and methods: Pre-TKI and post-TKI biopsies from 27 patients with an activating EGFR mutation were collected and analyzed for EGFR-T790M mutation, MET amplification, and SCLC transformation. Results: The T790M mutation was found in 16 patients (59%) whereas MET gene amplification was found in 2 (10.5%) of 19 evaluated cases. The histologic transformation from adenocarcinoma (ADC) to SCLC was identified in 3 patients (11%). In one of them reversal from SCLC back to adenocarcinoma was observed. One patient had the T790M mutation concordantly detected in 2 synchronous lesions whereas another patient showed T790M positivity only in one of 2 specimens. In 4 patients longitudinal biopsies revealed T790M gains and losses not always according to biological expectations. Conclusions: Intrapatient molecular or histologic heterogeneity may be frequently found during routine treatment of non-small cell lung cancer patients. This biological aspect may have profound repercussions on subsequent therapeutic decisions, and therefore requires in-depth investigation.