Why does cancer risk skyrocket exponentially after 60? A groundbreaking immunological model shows that thymic T-cell decline (half-life ~16 years) fits age-related cancer curves better than traditional mutation-accumulation theories across 101 cancer types (median R² = 0.956 vs. 0.947). Cancer may not be a slow mutation buildup—it might be a threshold phenomenon where tumors that arise throughout life suddenly escape control when thymic function drops below a critical point.