After synthesising different factors that determine T cell success against immunogenic cancer cells, we highlight that a possible unifying mechanism linking physical activity with improved T cell competency is the presence of elevated immunoregulatory cytokines – including the myokines IL-7 and IL-15 – in physically active people, which may be important in changing the trajectory of immunoediting by altering the fate of tissue-associated effector and regulatory T cells. This evidence concerns the gene IL15 and cancer.