Background and purpose: Data from randomized clinical trials in Scotland and Sweden testing the efficacy of tamoxifen therapy in patients with breast cancer have suggested that the drug may also reduce the risk of coronary heart disease. In view of these findings, we examined mortality from coronary heart disease among patients with early stage breast cancer who were enrolled in the National Surgical Adjuvant Breast and Bowel Project B-14 trial of tamoxifen therapy.
Methods: Deaths occurring among women who were randomly assigned to 5 years of either tamoxifen or placebo in the first phase of the B-14 trial were reviewed to determine the cause. Three categories of heart disease-related death were defined: 1) death from a definite fatal myocardial infarction, 2) death from definite fatal coronary heart disease/possible myocardial infarction, and 3) death from possible fatal coronary heart disease. Comparisons of the findings by treatment group were made on the basis of average annual hazard (i.e., death) rates and the corresponding relative hazard of death.
Results: The average annual death rate from coronary heart disease was lower for patients who received tamoxifen than for patients who received placebo, but the difference was not statistically significant. There were eight definite heart-related deaths (i.e., definite fatal myocardial infarction or definite fatal coronary heart disease/possible myocardial infarction) among the patients who received tamoxifen, yielding an average annual rate of 0.62 per 1000 patients. There were 12 definite heart-related deaths among the patients who received placebo, yielding an average annual rate of 0.94 per 1000. The corresponding relative hazard of death from definite fatal heart disease (tamoxifen versus placebo) was 0.66 (95% confidence interval = 0.27-1.61). Eleven deaths in the tamoxifen group and 10 deaths in the placebo group were classified as possible cases of fatal coronary heart disease. When these cases and the definite cases were considered together, the average annual death rate for the patients who received tamoxifen was 1.48 per 1000, and the rate for the patients who received placebo was 1.73 per 1000. The corresponding relative hazard of death was 0.85 (95% confidence interval = 0.46-1.58).
Conclusions: The findings from the B-14 trial are consistent with the findings from the Scottish and the Swedish trials, suggesting that tamoxifen treatment reduces coronary heart disease among patients with breast cancer. Continued follow-up of the patients in these trials and in ongoing prevention trials is needed to accumulate enough data so that reliable conclusions can be drawn about the benefits of tamoxifen in preventing heart disease.