Transformation from EGFR-mutant lung adenocarcinoma to small-cell lung cancer: from clonal evolution to lineage reprogramming

Abstract

EGFR-mutant lung adenocarcinoma (LUAD) that transforms into small-cell lung cancer (SCLC) following targeted therapy represents a clinically significant mechanism of acquired resistance, occurring in approximately 3–14 % of cases. This transformed variant, referred to as SCLC after transformation (SCLC-AT), follows an aggressive clinical course and carries a poor prognosis. SCLC-AT retains the original EGFR mutation but significantly down-regulates EGFR protein expression, eliminating its dependence on EGFR signaling while simultaneously acquiring a neuroendocrine phenotype. In nearly all cases, bi-allelic inactivation of both TP53 and RB1 is observed. In this overview, we provide a detailed examination of the molecular mechanisms underlying the transition from EGFR-mutant LUAD to SCLC. By integrating two primary biological concepts, clonal evolution and lineage reprogramming, we examine recent advances concerning the original cell or cells involved, as well as the genetic and epigenetic reprogramming and signaling pathway changes. While the transformation to SCLC is currently considered genetically and epigenetically irreversible, preclinical interventions targeting EZH2, AURKA, and DLL3 have shown potential in reversing the neuroendocrine phenotype or improving tumor immunogenicity. Future research should utilize single-cell and spatial multi-omics technologies to develop predictive models that can facilitate the early detection of impending transformation and guide precision therapies, ultimately enhancing patient outcomes.