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

OBJECTIVES: To assess whether there is an association between delivery of adjuvant chemotherapy to older women with breast cancer and development of dementia over time. DESIGN: Retrospective cohort study using Surveillance, Epidemiology, and End Results (SEER) data linked to Medicare claims data. SETTING: Women residing in geographic areas included in the SEER registry. PARTICIPANTS: 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. MEASUREMENTS: 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. RESULTS: 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). CONCLUSION: 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.