The role of chimeric antigen receptor (CAR) T cell therapy in breast cancer.
Breast cancer is one of the most common malignancies worldwide and remains a leading cause of cancer-related mortality. Over the past decades, advances in multimodal treatment have significantly improved patient survival. However, disease recurrence, metastatic progression, and therapeutic resistance continue to limit long-term outcomes, underscoring the need for more effective therapies. Among emerging immunotherapeutic approaches, chimeric antigen receptor T (CAR-T) cell therapy has attracted considerable attention. CAR-T therapy has achieved remarkable success in hematologic malignancies, prompting its investigation in breast cancer. However, translating this success to solid tumors remains challenging because of fundamental biological differences between hematologic and solid malignancies. Major barriers include antigen heterogeneity, limited tumor trafficking and infiltration, an immunosuppressive tumor microenvironment, and therapy-related toxicities. Numerous preclinical and clinical studies are currently evaluating CAR-T cell therapy in solid tumors, including breast cancer. These efforts incorporate next-generation CAR designs and novel engineering strategies with the goal of reproducing the clinical success achieved in hematologic malignancies. Although the available clinical evidence is still largely limited to early-phase trials, current findings suggest that CAR-T therapy in breast cancer is feasible and generally well tolerated. Most reported adverse events have been low-grade inflammatory toxicities, whereas severe neurotoxicity and dose-limiting toxicities have been infrequent. Despite this favorable safety profile, clinical responses remain modest, with stable disease representing the most common outcome and durable objective responses being uncommon. These findings underscore the need to overcome the major biological barriers that continue to limit CAR-T cell therapy in solid tumors. This review summarizes recent advances in CAR-T cell engineering, discusses the major target antigens investigated to date, provides a comprehensive overview of the available clinical evidence, and examines the key biological and clinical challenges that must be addressed to improve future therapeutic outcomes.