Review finds no single cause for apparent cancer–Alzheimer inverse association

A Mini Review in Frontiers in Endocrinology concludes that the modest, apparently bidirectional inverse association between cancer and Alzheimer’s disease is unlikely to have a single biological explanation. The authors distinguish population associations from tumor biology, systemic endocrine-treatment effects and molecular findings in experimental systems, noting that competing mortality, diagnostic surveillance, survivor selection, treatment exposure and the long preclinical courses of both diseases can distort observed risk.

Population evidence generally points toward lower dementia incidence after cancer and lower cancer incidence after dementia, although results differ by cancer type, dementia subtype, population and analytical design. In a cohort of 3,021,508 adults aged 60 or older, a previous cancer diagnosis was associated with a 25% lower subsequent dementia risk (HR 0.75, 95% CI 0.74–0.76). The association remained after adjustment for competing mortality (SHR 0.56, 95% CI 0.55–0.56), while Mendelian-randomization analysis yielded a smaller inverse association between genetically predicted cancer susceptibility and Alzheimer’s disease (OR 0.97, 95% CI 0.95–0.99). A bidirectional meta-analysis found 8% to 14% lower risks among cancer survivors for all-cause dementia, Alzheimer’s disease and vascular dementia, while dementia was associated with approximately 25% lower subsequent cancer risk.

These findings are sensitive to ascertainment and analysis. In UK Biobank, neither prevalent nor incident cancer was significantly associated with Alzheimer’s disease. All-cause dementia diagnoses rose during the first year after an incident cancer diagnosis (HR 1.83, 95% CI 1.42–2.36) before attenuating toward the null, a pattern compatible with detection bias caused by increased healthcare contact, treatment-related cognitive symptoms or diagnostic investigation. Rotterdam Study dementia estimates ranged from RR 0.71 to 1.10, depending on how cancer exposure, confounding, selective survival and death were addressed. Reduced screening after dementia, delayed diagnosis and long preclinical phases further complicate causal interpretation.

Evidence beyond diagnostic records nevertheless suggests a possible biological component. In a community autopsy cohort of 785 people, including 190 with a history of cancer, cancer was associated with lower odds of advanced Braak neurofibrillary-tangle stages (OR 0.38, 95% CI 0.26–0.55), neuritic plaques (OR 0.52, 95% CI 0.36–0.75) and cerebral amyloid angiopathy, but not with TDP-43, α-synuclein or cerebrovascular pathology. Genetic-correlation and transcriptome-wide association analyses also identified opposing associations across Alzheimer’s disease and several cancers involving cell-cycle regulation, apoptosis, DNA-damage responses and metabolism. The pattern is not uniform across neurodegenerative disorders, including Parkinson’s disease and melanoma, so it does not support a universal cancer–neurodegeneration antagonism.

Breast and prostate cancers illustrate why tumor effects must be separated from endocrine treatment. Estrogen- and androgen-receptor signaling supports tumor growth while also regulating neuronal metabolism, mitochondrial function, synaptic activity, vascular homeostasis and inflammation. Among 70,701 Korean breast cancer survivors, Alzheimer’s disease risk was 8% lower than among 180,265 controls (SHR 0.92, 95% CI 0.86–0.98), but the association did not persist in landmark analyses restricted to more than five years of survival. A Swedish study of 26,741 five-year survivors found no overall association with dementia, Alzheimer’s disease or vascular dementia, although diagnosis after age 65 was associated with a 35% higher Alzheimer’s disease risk (SHR 1.35, 95% CI 1.05–1.75).

Treatment findings are also heterogeneous. In a US claims cohort of 57,843 women with breast cancer, hormone-modulating therapy was associated with lower Alzheimer’s disease incidence (RR 0.82, 95% CI 0.75–0.90) and dementia incidence (RR 0.88, 95% CI 0.83–0.93). A SEER–Medicare analysis of 18,808 women aged 65 or older found a smaller reduction in Alzheimer’s disease and related dementias (HR 0.93, 95% CI 0.88–0.98), varying by age, race and treatment class. For prostate cancer, a meta-analysis of 28 studies with approximately 2.54 million participants associated androgen-deprivation therapy with 20% higher all-cause dementia risk (HR 1.20, 95% CI 1.11–1.29) and 26% higher Alzheimer’s disease risk (HR 1.26, 95% CI 1.10–1.43). Individual cohorts have not consistently reproduced these associations, so the pooled findings do not establish causality.

The review describes overlapping insulin/IGF–PI3K–AKT, mTOR, AMPK, mitochondrial, cell-cycle, chaperone and autophagy–lysosomal pathways with context-dependent consequences. Tumors use them for metabolic adaptation, proliferation, apoptosis resistance and proteotoxic-stress tolerance, whereas Alzheimer’s disease involves energetic failure, impaired proteostasis and neuronal degeneration. Evidence comes mainly from human tissue, cancer-cell systems, organoids and animal models rather than direct studies of people with both diseases, making these biologically plausible contributors rather than demonstrated explanations of inverse comorbidity.

Protein self-assembly provides another possible bridge. In Alzheimer’s-model mice, lung, prostate and colon tumors secreted cystatin C, which interacted with amyloid-beta and activated TREM2-dependent microglial clearance. Disrupting TREM2 or mutating cystatin C eliminated the effects, establishing causality in that experimental system. Other preclinical studies found that amyloid-beta, human islet amyloid polypeptide and calcitonin could alter cancer-cell fitness, but uncertain physiological concentrations, aggregation states and selectivity over nonmalignant cells limit interpretation. Human plasma findings do not support a straightforward systemic anticancer effect, and melanoma-secreted amyloid-beta has promoted brain metastasis experimentally.

The bounded conclusion is that inverse comorbidity may reflect interacting epidemiological, endocrine, metabolic, proteostatic and protein-assembly mechanisms rather than one pathway. The authors recommend treatment-aware longitudinal studies that distinguish cancer subtype and stage from treatment class, dose and duration; incorporate amyloid and tau biomarkers, neuroimaging, endocrine markers and metabolic profiles; and test molecular interactions at physiologically relevant concentrations and aggregation states in patient-derived organoids, immune-competent cocultures and animal models. Whether the tumor-derived cystatin C–TREM2 pathway or other preclinical mechanisms contribute materially to inverse comorbidity in humans remains unknown.

Subject of Research: Epidemiological and experimental evidence on inverse comorbidity between cancer and Alzheimer’s disease

Article Title: Cancer–Alzheimer inverse comorbidity from epidemiology to protein self-assembly

Article References: Zhang, Y., Wang, L., Wei, J., Shuzan, N., & Zheng, J. (2026). Cancer–Alzheimer inverse comorbidity from epidemiology to protein self-assembly. Frontiers in Endocrinology, 17, Article 1992522. https://doi.org/10.3389/fendo.2026.1992522

Image Credits: AI Generated

DOI: 10.3389/fendo.2026.1992522

Keywords: cancer, Alzheimer’s disease, inverse comorbidity, epidemiology, endocrine therapy, amyloid-beta, protein self-assembly, proteostasis, dementia risk, Alzheimer, inverse, comorbidity