RLY-5836 + abemaciclib + fulvestrant

RLY-5836 + abemaciclib + fulvestrant is an investigational combination therapy being explored for the treatment of advanced or metastatic hormone receptor-positive, HER2-negative breast cancer with documented PIK3CA mutation. RLY-5836 is a small molecule, oral, allosteric, pan-mutant, and isoform-selective inhibitor of phosphoinositide 3-kinase alpha (PI3Kα) developed by Relay Therapeutics, targeting cancers driven by activating PIK3CA mutations. Abemaciclib is an oral, potent, and selective small molecule inhibitor of cyclin-dependent kinase 4 and 6 (CDK4/6), approved for metastatic breast cancer, where it causes sustained cell-cycle arrest. Fulvestrant is a selective estrogen receptor degrader (SERD) that antagonizes and degrades the estrogen receptor, reducing estrogen-driven cancer cell growth. The triple combination is designed to target key oncogenic pathways: PI3K signaling (PIK3CA mutations), cell cycle progression (CDK4/6), and hormone receptor signaling (estrogen receptor), aiming to delay progression and overcome resistance to endocrine therapies.