Tamoxifen prevents recurrence after
breast cancer and
breast cancer among high-risk women, and may prevent
myocardial infarction (MI). To assess the impact of
tamoxifen on MI risk, we conducted a case-control study of first MI after
breast cancer nested among women diagnosed with
breast cancer, while enrolled in a health maintenance organisation from 1980 to 2000. We obtained information on
breast cancer treatment and MI risk factors through medical record reviews and interviews. Data were analysed using conditional logistic regression. Of 11,045 women with
breast cancer, 134 met MI criteria and were matched to two MI-free control subjects on year of birth and
breast cancer diagnosis. After adjusting for smoking,
hypertension and diabetes,
tamoxifen was unassociated with MI (odds ratio (OR)=1.2, 95% confidence interval (CI)=0.7-1.9). Duration, cumulative dose and recency of use were not associated with MI.
Radiation therapy was associated with MI (OR=2.0, 95% CI=1.1-3.5), an association that varied slightly but not statistically significantly by
tamoxifen use (radiation with
tamoxifen, OR=2.0, 95% CI=0.9-4.4; radiation without
tamoxifen, OR=2.9, 95% CI=1.2-7.5).
Tamoxifen treatment for
breast cancer does not appear to increase or decrease MI risk, although
radiation therapy appears to increase MI risk.