Lineage Plasticity and Histologic Transformation in EGFR-TKI Resistant Lung Cancer

Lineage plasticity, the ability of cancer cells to alter their differentiated state through transcriptional and epigenetic reprogramming, has emerged as a key mechanism of therapeutic resistance across cancers. This adaptive process can manifest in multiple ways, including epithelial-mesenchymal transition, acquisition of stem-like features, and histological transformation, the most striking and clinically apparent example. In EGFR-mutant lung adenocarcinoma (LUAD), lineage plasticity is increasingly recognized as a prevalent mechanism of acquired resistance to tyrosine kinase inhibitors (TKIs). Among its visible manifestations, histologic transformation into small-cell lung cancer (SCLC) is the most frequent, while squamous transformation and other phenotypic shifts also occur. Transformed tumors typically retain the initiating EGFR mutation but lose EGFR dependence, acquire neuroendocrine features, and display aggressive clinical behavior with poor clinical outcomes compared with both de novo SCLC and non-transformed LUAD. Recent studies show that plasticity arises through combined genomic, transcriptomic, and epigenetic reprogramming, often foreshadowed by molecular alterations before overt histological change. Spatial and single-cell profiling reveal heterogeneous trajectories and intermediate states, while functional models and multi-omics approaches have begun to identify therapeutic vulnerabilities distinct from both de novo EGFR-mutated SCLC and classical EGFR-mutated LUAD. Thus, lineage plasticity, whether manifested as histologic transformation or through more subtle epigenetic reprogramming, represents a formidable resistance mechanism in NSCLC. Defining its molecular basis and temporal dynamics will be essential for early detection, prognostication, and the development of tailored therapies.