Novel ETV1 mutation in small cell lung cancer transformation resistant to EGFR tyrosine kinase inhibitors.

Abstract

e20568 Background: Non-small cell lung cancer (NSCLC) patients harboring mutations in the epidermal growth factor receptor (EGFR) gene dramatically respond to EGFR tyrosine kinase inhibitors (TKIs). However, these patients inevitably developed acquired resistance to TKIs. Among them, small cell lung cancer (SCLC) transformation is a relatively rare mechanism of resistance. However, the mechanism of SCLC transformation is largely unclear. Methods: We performed a 639 cancer-relevant gene panel to detect genetic differences of tissues before and after TKIs resistance caused by SCLC transformation. In vitro experiments were conducted to study the role of ETS variant transcription factor 1 (ETV1) on SCLC transformation and TKIs resistance. Results: We present two EGFR-mutant pulmonary adenocarcinoma (ADC) patients. One with EGFR exon 19 deletion (Ex19del) accepted first-line gefitinib treatment and then received osimertinib(AZD9291) treatment due to acquisition of EGFR-T790M mutation. A novel ETV1 mutation (p.P159S) was detected in SCLC samples after SCLC transformation when not coexisting with T790M. Another patient harbored an EGFR exon 21 mutation (p.L858R) with a long-lasting response to first-line gefitinib and then transformed to SCLC. A previously unreported ETV1 mutation (p.E462Q) was detected in SCLC tissue. In vitro, ETV1 p.E462Q and p.P159S mutations participated in neuroendocrine differentiation by inducing the expression of the neuroendocrine transcription factor, achaete-scute homolog 1 (ASCL1) and promoted H69 cells proliferation. Besides, ETV1 p.E462Q and p.P159S mutations were resistant to first-generation (gefitinib) and third-generation (osimertinib) TKIs after introducing into NCI-H358 cells. Conclusions: Novel ETV1 p.E462Q and p.P159S mutations were found in SCLC tissues of TKIs resistant patients, providing novel understanding of ETV1 involved in acquired resistance to EGFR-TKIs via SCLC transformation.