Risk of Dementia in Older Breast Cancer Survivors: A Population-Based Cohort Study of the Association with Adjuvant Chemotherapy

To assess whether there is an association between delivery of adjuvant chemotherapy to older women with breast cancer and development of dementia over time. Retrospective cohort study using Surveillance, Epidemiology, and End Results (SEER) data linked to Medicare claims data. Women residing in geographic areas included in the SEER registry. Women aged 66 to 80 diagnosed with non-metastatic invasive breast cancer from 1992 to 1999 were included. It was determined whether patients had undergone chemotherapy within 6 months of diagnosis. Whether women developed dementia over time was determined using diagnostic codes. The effect of adjuvant chemotherapy on development of dementia was evaluated, adjusting for confounders using a proportional hazards model stratified for age. Twenty-one thousand three hundred sixty-two women met selection criteria; 2,913 received chemotherapy, and 18,449 did not. Women who received chemotherapy were younger than those who did not (median aged 70 vs 73; P <.001). Median follow-up time was 59 months. After controlling for other factors, it was found that chemotherapy was not associated with a greater risk of development of dementia over time for any age group (hazard ratio for dementia in women receiving chemotherapy: aged 66-70=0.83, 95% confidence interval (CI)=0.48-1.45, P=.5; aged 71-75=0.74, 95% CI=0.46-1.18, P=.2; aged 76-80=0.49, 95% CI=0.28-0.88, P=.02). Receipt of chemotherapy in older women with breast cancer was not associated with a greater risk of dementia diagnosis over time; very elderly women who undergo chemotherapy may be at lower baseline risk. The use of a claims-based definition of dementia limited the study.