Hypertension and breast cancer risk in a 19-year follow-up study (the DOM cohort). Diagnostic investigation into mammarian cancer.

BACKGROUND: To investigate whether hypertension and the use of anti-hypertensive drugs are associated with breast cancer risk.
METHODS: This was a prospective study of 11, 011 women living in Utrecht, the Netherlands, aged 50-65 years at enrolment in a breast cancer screening project (DOM cohort). Women attended screening rounds between 1974 and 1985 at which blood pressure was measured and information on drug use and breast cancer risk factors was ascertained. Since 1974 (median follow-up time 19 years), information on breast cancer occurrence and death has been registered. Hypertension was defined as a systolic blood pressure > 160 mmHg or a diastolic blood pressure > 95 mmHg or current use of drugs for the indication hypertension. Cox's regression analysis was used to investigate the association between hypertension (treated or untreated) and subsequent breast cancer risk. Analyses were adjusted for age, body mass index, height, parity, familial breast cancer, smoking and oral contraceptive use.
RESULTS: A total of 523 women were diagnosed with breast cancer. Hypertensive women experienced a statistically significant increased breast cancer risk of 23% (age-adjusted hazard ratio (HRa) = 1.23; 95% confidence interval (CI) 1.01 -1.49). After adjustment for all confounders, the increase was 14% (HR = 1.14; 95% CI 0.93-1.40). The decline in risk was mainly attributable to the effect of BMI. The risk was similar in treated (HR = 1.22; 95% CI 0.91-1.63) and untreated hypertensive women (HR = 1.13; 95% CI 0.91-1.40).
CONCLUSION: These results do not support an association between hypertension and breast cancer, and if there is a link, it is likely to be positive and relatively small in size (+14%). This relation, if present, is not attributable to anti-hypertensive drugs, since the relation is also present in non-drug users.