Cancer

Cancer is the class of diseases in which a somatic cell lineage escapes the controls on its own division and invades tissue that is not its own. It is among the leading causes of death worldwide, and it is the disease whose incidence climbs most sharply with age. That combination puts it at the centre of nearly every argument this wiki makes about extending human life: it is the ceiling that life-extension arithmetic runs into, the risk that cell and gene therapies have to price in, and the reason two of the Hallmarks of aging are usually explained as tumour suppression in the first place.

§An age-related disease

Cancer incidence rises as a steep power of age. Armitage and Doll fitted that relationship in 1954 and read the log-log slope as evidence that carcinogenesis requires six or seven rate-limiting steps in a single cell lineage, which is why risk accumulates rather than arriving at a threshold.¹ The multi-stage picture has been refined repeatedly since, but the demographic fact it was built on has not moved: most cancers are diagnosed in people over 65, and the age curve is the single strongest predictor in oncology.

The pattern is not uniform. The American Cancer Society's 2026 statistical report projects roughly 2.1 million new US cases and 626,000 deaths, with 12% of diagnoses in people under 50 and colorectal cancer incidence in that group rising year on year.² Part of the most recent acceleration is attributed to screening beginning at 45 rather than 50, which finds disease earlier without changing how much of it there is; the longer-running rise that preceded the change in screening age is not accounted for that way. Early-onset disease is a reminder that "cancer is a disease of aging" describes a rate, not a rule.

Why this matters here

Eliminating every cancer death would add roughly three years to US life expectancy at birth, because the people saved would die of something else soon afterwards.³ That figure is the origin of the geroscience argument: attacking one disease at a time buys little, because the underlying risk is shared. It also sets the constraint in the other direction. Any intervention that slows aging must not raise cancer incidence, because cancer is the failure mode with the shortest fuse.

§The mechanism

Cancer is somatic evolution: mutation supplies variation, and clonal selection does the rest. The surprise of the last decade is how much of the first half is already present in healthy tissue. Ultra-deep sequencing of normal, sun-exposed human eyelid skin found mutation burdens comparable to those in many tumours, with drivers of squamous cell carcinoma under strong positive selection in a substantial fraction of ordinary skin cells. Similar clonal expansions appear in normal oesophagus, endometrium and blood. In blood the phenomenon has a name and a prognosis: clonal haematopoiesis, present in a rising share of people through later life, carries an elevated risk of blood cancer and, unexpectedly, of cardiovascular death.⁴ Mutation is therefore necessary and nowhere near sufficient. What separates a large mutant clone from a tumour is the tissue context that lets it keep going, which is the same context that ages.

The capabilities a cell must acquire were codified by Hanahan and Weinberg in 2000 and extended twice since. The 2022 revision added phenotypic plasticity, non-mutational epigenetic reprogramming, polymorphic microbiomes, and senescent cells as further dimensions.⁵ Two of those overlap directly with the aging literature: the epigenetic changes that clocks measure, and the arrested cells described under Cellular senescence.

§Peto's paradox

If every cell division carries a risk of transformation, a whale should be riddled with tumours and a mouse should be almost immune. Peto noticed in 1975 that cancer incidence across species tracks neither body size nor lifespan, an observation now called Peto's paradox. Large, long-lived animals must therefore have evolved additional suppression. Some of it has been found: African elephants carry about twenty copies of the tumour-suppressor gene TP53 against a human single copy, and their cells commit to apoptosis more readily after DNA damage.⁶ Naked mole-rats, one of the animals discussed under Negligible senescence, resist tumours by other means again.

The paradox is genuinely encouraging for the field: cancer suppression is evolvable, adjustable, and evidently not at its ceiling in humans. It is also a caution. Everything comparative biology has turned up so far is germline architecture built over millions of years, not a module that can be added to an adult body.

§Where longevity work meets oncology

Most proposals for slowing or reversing aging touch cancer risk somewhere, and usually in both directions.

Telomerase. Nearly all human tumours restore telomere maintenance, so the attrition described under Telomeres and telomerase is a real tumour-suppressive barrier, and the division limit Hayflick found in cultured human cells is one of the things standing between a mutant clone and a tumour. Mendelian randomization studies find that inherited longer telomeres raise the risk of several cancers. Adding telomerase across an adult body means pushing on a trait that selection appears to have already compromised.

Senescence. The arrest is antagonistic pleiotropy in its clearest form. It stops damaged cells from becoming tumours; the secretory phenotype it produces then promotes tumour growth in the surrounding tissue. Clearing senescent cells therefore has a plausible anti-cancer rationale and a plausible pro-cancer one, and the human trials run so far have been too small and too short to speak to either.

Reprogramming. Continuous expression of the Yamanaka factors produces teratomas in mice, which is why the field works on transient, partial protocols and why the dose-and-duration question is a safety question rather than an optimisation one. Epigenetic reprogramming is the intervention class in which the cancer risk is most explicitly the rate-limiting problem.

Growth signalling. People with growth hormone receptor deficiency have been reported to develop cancer and diabetes at strikingly low rates without living longer,⁷ which is the cleanest human hint that dialling down growth signalling trades disease incidence against something else. Rapamycin inhibits a pathway that oncology already targets, and Metformin and the TAME trial's observational cancer signal is one of the reasons it was proposed as a geroprotector at all.

Delivered genes and cells. Insertional mutagenesis is the classic hazard of Somatic gene therapy, and it is not historical: in January 2024 the US Food and Drug Administration required a boxed warning about T-cell malignancies on every approved CAR-T product.⁸ The off-target and structural consequences of editing carry the same concern into the CRISPR era.

Would slowing aging reduce cancer?

The geroscience prediction is that it would, because a younger tissue environment suppresses clonal expansion and a competent immune system removes transformed cells. The counter-argument is that several mechanisms proposed as geroprotective — telomere maintenance, senescence clearance, restored stem-cell proliferation — are the same mechanisms tumours exploit. No human trial has been powered to settle it, and the mouse evidence points both ways depending on the strain and the intervention.

§What has actually worked

The US cancer death rate has fallen by about a third from its 1991 peak, an estimated 4.8 million deaths averted.² Most of that is not new biology. It is the collapse in smoking, and after it screening and better conventional treatment.

Immunotherapy is the genuine mechanistic addition. Checkpoint blockade moved from a survival signal in metastatic melanoma to standard care across several tumour types within a decade, and engineered T cells produced remission rates in relapsed paediatric leukaemia that chemotherapy had not.⁹ Both are also the source of the safety signals above, and neither works for most patients with most cancers.

Screening is where the field's own evidence is least comfortable. South Korea's thyroid cancer incidence rose sharply after ultrasound screening spread, with no matching change in thyroid cancer mortality, the clearest documented case of overdiagnosis in oncology. Multi-cancer early detection tests, which look for tumour-derived DNA in blood, are the current version of the same hope and the same question; the first large prospective study reported test performance and diagnostic workload rather than any effect on deaths.¹⁰ Detection is not the same as benefit, a distinction that recurs throughout Consumer blood testing and biomarker work.

§Open problems

Metastasis, not the primary tumour, is what kills in the large majority of cases, and it remains the least tractable part of the disease. Resistance is an evolutionary process rather than a pharmacological one, which is why durable responses are rarer than initial ones. Prevention research attracts a small share of cancer funding, which many in the field argue is the wrong allocation given that most of the mortality decline so far came from people not starting to smoke rather than from anything given to a patient.

Survivorship is the problem success created. Chemotherapy and radiation damage gonadal tissue, so freezing eggs, sperm or embryos through IVF before treatment is now routine for patients of reproductive age. Cytotoxic therapy also drives cells into the arrested state described above, which is one proposed source of the accelerated functional decline reported in long-term survivors.

For the arguments this wiki tracks, the unresolved question is narrower and sharper. Nobody has shown, in humans, that an intervention aimed at aging changes cancer incidence in either direction. Until a trial is run long enough and large enough to measure it, claims about radical life extension are claims about a body whose dominant late-life failure mode has not been addressed. Cancer is reported to be an uncommon cause of death among the oldest people on record, which some read as evidence that late-life cancer risk plateaus and others read as evidence that they died of something faster first.

§See also

• Hallmarks of aging
• Cellular senescence
• Telomeres and telomerase
• Geroscience hypothesis
• Immunosenescence
• Senolytics
• Somatic gene therapy
• Compression of morbidity

§References