Liquid biopsies for detection, characterization, and interception of therapy resistance in thoracic malignancies

Therapy resistance remains a leading cause of treatment failure and mortality in thoracic malignancies, despite major advances in targeted therapies and immunotherapies. Resistance evolves through heterogeneous, patient-specific mechanisms, including genetic alterations, epigenetic reprogramming, lineage plasticity, and tumor-microenvironment interactions, often emerging before radiographic progression or clinical relapse. Conventional tissue biopsies and imaging, while essential for diagnosis and treatment selection, are limited in their ability to capture spatial and temporal tumor heterogeneity or to support dynamic monitoring of tumor evolution. Liquid biopsy has therefore emerged as a minimally invasive approach for real-time assessment of tumor-derived biomarkers in circulation, enabling longitudinal tracking of resistance biology across the cancer care continuum. In this review, we highlight recent advances in liquid biopsy applications for thoracic malignancies, focusing on circulating tumor DNA (ctDNA) and circulating tumor cells (CTCs) as complementary analytes for baseline molecular profiling, detection of primary and acquired resistance to therapy, and identification of minimal residual disease and molecular relapse. Beyond mutation-based approaches, we highlight emerging non-genomic ctDNA features, including epigenomic and fragmentomic signatures, that capture treatment-induced adaptation and lineage plasticity not detectable by conventional plasma genomic profiling, and discuss advances in CTC technologies that preserve cellular and phenotypic context relevant to resistance and metastatic potential. Finally, we examine multimodal liquid biopsy strategies that integrate multiple circulating analytes with artificial intelligence-assisted methods to enhance sensitivity, provide a more comprehensive view of tumor biology, and inform adaptive therapy strategies. We also outline key analytical and clinical challenges that must be addressed through standardized, prospective trials to translate liquid biopsy-guided surveillance and early interception of resistance into improved patient outcomes.