Age at incident treatment of hypertension and risk of cancer: a population study

To determine the effect of treated hypertension on the risk of cancer. Population based external comparison study using the Saskatchewan Health databases. A total of 42,270 subjects were followed for a median of 17.9 years after initiating antihypertensives for hypertension. The effect of hypertension on the risk of cancer varied significantly by age (interaction p < 0.001). Compared with the general population, subjects under 60 years at the time of initiation of antihypertensives had a significantly increased risk of cancer (RR 1.34, 95% CI 1.18-1.52 adjusted for age, sex, and calendar year) while subjects over 60 had a significantly decreased risk (RR 0.88, 95% CI 0.78-0.98). Similar results were obtained for cancer death outcomes. In each subgroup, relative risks across most cancer sites were similar in magnitude and direction. Results were essentially unchanged when analyses were restricted to cancers diagnosed after the first 10 years of follow-up. The effect of treated hypertension on cancer risk varies by the age at incident treatment of hypertension. These findings are not a result of reverse causality or detection bias. However, they may in part be a consequence of residual confounding and/or reflect the type of hypertension being treated.