Why 90-Year-Olds Get Less Cancer

TL;DR

Cancer incidence drops in people 85+ likely because aging cells divide slower, senescent cells can't turn cancerous, and carcinogen exposure decreases after retirement.

Key Points

• 1.Cancer risk generally rises with age but reverses after 85. A 2017 paper found cancer incidence declines in the 'oldest-old' (85+), despite them having more accumulated mutations, weakened immune systems, and longer carcinogen exposure — the opposite of what you'd expect.
• 2.A 2025 Stanford/UPenn mouse study confirmed older mice get less cancer. Aged mice (21 months) given identical KRAS-induced lung cancer had 2–3x fewer tumors and 4–5x fewer cancerous cells than young mice (5 months), with significantly smaller tumor sizes.
• 3.Tumor suppressor genes like PTEN were surprisingly less active in older mice, not more. Knocking out PTEN caused tumors in younger mice to grow 2x more than older ones, suggesting something else in the PI3K-AKT signaling pathway weakens with age to slow cancer growth.
• 4.Senescent cells — permanent non-dividing retirees — may explain fewer tumors in the elderly. These cells accumulate with age and cannot be reprogrammed into cancer cells, providing a passive protective effect, though they can also release chemicals that paradoxically increase cancer risk.
• 5.Reduced carcinogen exposure after retirement accounts for some of the decline. Between 2–8% of cancers are occupational; by 80, most people have retired or entered care facilities with fewer environmental carcinogens like tobacco, and slower cell division limits tumor growth across all cell types.