Abstract
Resistance to tyrosine kinase inhibitors (TKIs) in non-small cell lung carcinoma (NSCLC) remains a significant clinical challenge. Osimertinib, a third-generation TKI, has demonstrated efficacy in overcoming resistance, but novel resistance mechanisms continue to emerge. This case report presents a unique instance of histologic transformation from NSCLC to carcinosarcoma, representing a previously unreported manifestation of osimertinib resistance. We describe the clinical course of a 63-year-old female with epidermal growth factor receptor (EGFR)-mutant NSCLC who initially responded to osimertinib but eventually developed carcinosarcoma. The transformation was associated with additional EGFR mutations and alterations in RB and TP53. Despite aggressive treatment, the patient's condition deteriorated, emphasizing the limited therapeutic options for carcinosarcoma. This case underscores the need for further research to elucidate the molecular mechanisms behind histologic transformation and explore novel therapeutic strategies to address osimertinib resistance in NSCLC. Understanding and addressing these mechanisms are crucial for improving outcomes in patients facing this challenging form of resistance.