Old Hosts, Young Models: Rethinking Cancer Immune Evasion in Aging.

Cancer is largely a disease of older adults, yet the framework used to explain how tumors evade immunity was built almost entirely on young, specific-pathogen-free mouse models and on clinical trials that under-enroll older adults. This review examines whether that framework holds when the host is old. Rather than surveying cancer immunology and aging comprehensively, it focuses on one question: whether the four host capacities the standard account of immunoediting and checkpoint blockade assumes still hold in the aged host. These are a naive T-cell repertoire wide enough to generate tumor-specific clones, a stromal environment that does not suppress priming, functional natural killer [NK] cell surveillance, and an immune baseline free of chronic inflammation. Aging alters all four, but not uniformly. Thymic involution and NK cell decline result in the immune system operating at reduced capacity, representing a shift in severity rather than a fundamental change in mechanism. The NK cell axis is disproportionately significant, as no approved therapies currently restore its function. In contrast, aged stromal senescence and inflammaging represent qualitative changes: the tissue environment becomes suppressive prior to tumor development, rather than as a consequence of tumor presence. The clinical evidence neither confirms nor refutes this interpretation. Older and younger patients gain similar benefit from checkpoint blockade, which is easily read as age being immunologically irrelevant. We argue instead that chronological age bundles aging changes acting on response in opposite directions. What predicts response is more accurately captured by immunological age than by chronological age. This reframing has a clear translational consequence. Therapeutic approaches should not only target the release of suppressed immune responses but also address the correction of the aged microenvironment. This hypothesis is currently being evaluated by senolytic strategies, which have been tested in an initial clinical trial and are supported by converging preclinical evidence.