Post-Stroke Cancer Risk among Postmenopausal Women: The Women's Health Initiative

Associations between a history of cancer and higher subsequent stroke risk have been established. However, whether a history of stroke is associated with higher subsequent cancer risk, especially for cancers with overlapping risk factors for stroke, is unknown. Therefore, we examined whether a history of stroke was associated with subsequent cancer risk and tumor site, by race/ethnicity, among postmenopausal women.

Using data from 145,075 participants in the Women's Health Initiative observational study and clinical trials (1993-2014), we used Cox proportional hazards models to predict cancer risk, comparing women with and without a history of stroke. Bivariate and multivariate models were estimated, accounting for potential confounders and death as a competing risk.

Women with a history of stroke survived roughly 3 fewer years than women without such history. The average time between incident stroke and incident cancer was 4.8 years. In adjusted competing risk models, women with a history of stroke had a lower cancer risk compared with women without such a history (adjusted hazard ratio, 0.81; 95% CI, 0.75-0.88). The magnitude of the association between a history of stroke and time to incident cancer was similar across racial/ethnic groups.

Postmenopausal women with a history of stroke had a significantly lower risk of subsequent cancer compared with women with no history of stroke. Although the risk of certain cancers were greater for African American compared with White women, the association between a stroke history and cancer risk did not vary by race/ethnicity.

Postmenopausal women with a history of stroke, who survive long enough to develop cancer, have a lower risk of cancer than women without such a history. Future studies should examine whether behavioral or clinical characteristics explain and/or mediate this association.