Hot flashes are a common symptom among women during their menopause transition, likely due to the changes of endogenous hormone levels. Previous research suggested that hot flashes symptoms were associated with a reduced risk of cardiovascular diseases. Few studies have investigated the association of hot flashes symptoms with the risk of breast cancer. Furthermore, the confounding effect by hormone use has not been sufficiently addressed in previous studies.

We investigated the association between hot flashes symptoms and risk of postmenopausal breast cancer in the Nurses’ Health Study (NHS). In order to eliminate the confounding by hormone use, we investigated the association only among women who never used hormone therapy. We calculated relative risk of breast cancer using a multivariate Cox model, adjusting for potential confounders, including age, race, family history of breast cancer, age at menarche, age at menopause, parity, age at first birth, body mass index, smoking, alcohol use, and education. We further investigated the severity of hot flashes symptoms in association with risk of postmenopausal breast cancer.

We documented 1079 incidence of breast cancer during 396,166 person-years of follow-up. Hot flashes symptoms were not associated with risk of postmenopausal breast cancer after adjustment for potential confounders (RR = 1.02, 95% CI, 0.90- 1.15) among non-users of hormone therapy. Relative risk of breast cancer across symptom severity categories (mild, moderate, severe) were 1.01 (95% CI, 0.87-1.17), 1.04 (95% CI, 0.88-1.22), and 1.05 (95% CI, 0.75-1.46), respectively.

These data suggested that menopausal symptoms were not associated with risk of postmenopausal breast cancer.