NK cells in breast cancer.

Natural killer (NK) cells are effectors of innate antitumor immunity, yet their therapeutic potential in solid tumors remains largely unrealized. Breast cancer exemplifies this paradox: NK cells are present in circulation and detectable within tumors, but their cytotoxic activity is limited. Recent advances in single-cell and spatial profiling reveal that NK-cell failure in breast cancer does not result from simple immune absence but from multilayered constraints imposed by the tumor ecosystem. Soluble mediators, metabolic pressures, stromal architecture, and suppressive immune networks reprogram NK-cell identity and uncouple activation from cytotoxicity. Understanding how these constraints shape NK-cell states reframes breast cancer as a model of innate immune dysfunction and highlights new opportunities to reestablish NK-cell function through immunotherapies.