As the thymus gland quietly fades with age, so too does the immune system's capacity to recognize and resist cancer — a vulnerability that has long undermined immunotherapy in older patients. Researchers have now identified thymulin, a peptide the thymus produces in diminishing quantities over a lifetime, as a potential means of reversing the inflammatory drift that corrupts the tumor microenvironment in aged bodies. In mouse models of breast cancer, thymulin suppressed the pro-inflammatory myeloid cells that accelerate tumor growth and restored the effectiveness of checkpoint immunotherapy dr