Incidence of breast cancer among postmenopausal, hypertensive women.

Elevated blood pressure has been proposed to be a risk factor for breast cancer but the results remain controversial. In this study, the incidence of breast cancer among 9,112 postmenopausal, hypertensive women included in the community-based hypertension register of the North Karelia project was assessed through the Finnish Cancer Registry. The mean follow-up time was 27 years. The incidence of breast cancer in hypertensive women in our cohort was similar to the age and period specific population-based rates for Eastern Finland [the standardised incidence ratio 0.96 (95% confidence interval 0.86-1.05)]. In the Cox regression analysis, there was no association between blood pressure levels, or use of antihypertensive (AH) drugs, and breast cancer incidence, when all women were considered. There was a statistically significant interaction of the use of AH drugs at baseline and the diastolic blood pressure (DBP). Among women who were not using AH drugs at baseline, the DBP level was positively associated with the subsequent risk of breast cancer (hazard ratio 1.26/10 mm Hg, 95% confidence interval 1.06-1.46). In women with AH drugs at baseline, the DBP had an opposite effect of borderline significance (hazard ratio 0.90/10 mm Hg, 95% confidence interval 0.78-1.01). In conclusion, breast cancer incidence among postmenopausal hypertensive patients in general does not differ from that of general population. Elevated DBP levels may be associated with an increased breast cancer risk among nonpharmacologically treated women.