Hypertension, antihypertensive medication use, and breast cancer risk in the California Teachers Study cohort.

<bold>Background: </bold>We investigated the association between hypertension, antihypertensive (AH) medication use, and breast cancer in a large prospective study, the California Teachers Study (CTS).<bold>Methods: </bold>Information on history of hypertension and lifetime regular use of AH medications was collected from 114,549 women in 1995-1996. Among them, 4,151 invasive breast cancers were diagnosed between 1995 and 2006. Additional information on AH use was collected from 73,742 women in 2000-2001, and 1,714 of these women were subsequently diagnosed with breast cancer. Cox proportional hazards regression was used to estimate relative risks (RR) and 95% confidence intervals (CI) for breast cancer.<bold>Results: </bold>Use of AH medication for ≥5 years, when compared with no use, was associated with a modest increased risk of invasive breast cancer (RR = 1.18, 95%CI 1.02-1.36). This increased risk appeared to be confined to estrogen receptor (ER)-positive tumors (RR = 1.21, 95%CI 1.03-1.43) and pre-/peri-menopausal women (RR = 1.58, 95%CI 1.11-2.25).<bold>Conclusions: </bold>Increased risk of invasive breast cancer was observed for long-term (≥5 years) AH use, and this appeared to be confined to ER + breast cancer and younger women. [ABSTRACT FROM AUTHOR]