Next-generation CDK inhibitors in HR+/HER2- breast cancer.

Cell-cycle dysregulation is a central driver of breast cancer progression and a major therapeutic vulnerability, particularly in hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-) disease. The clinical success of cyclin-dependent kinase (CDK) 4/6 inhibitors combined with endocrine therapy has transformed treatment paradigms and established cell-cycle targeting as a cornerstone of care. However, important challenges remain, including hematologic toxicity, incomplete and largely cytostatic responses, and the near-universal development of resistance. These limitations have highlighted the need for next-generation CDK-directed strategies capable of improving selectivity, extending disease control, and overcoming adaptive escape pathways. This Review examines the evolving landscape of CDK-targeted therapeutics in breast cancer, with particular emphasis on emerging CDK4-selective inhibitors, CDK2-directed approaches, and broader multi-CDK strategies. We discuss the biological rationale underpinning these agents, the mechanisms of resistance that have informed their development, and the clinical opportunities they may create across both advanced and early-stage settings. By refining target specificity and addressing resistance-associated cell-cycle rewiring, next-generation CDK inhibitors may reduce toxicity, enhance treatment durability, and enable more effective combination and sequencing strategies. Collectively, these advances promise to move breast cancer treatment beyond current CDK4/6 inhibition toward more precise, adaptable, and durable cell-cycle-directed therapy.