Reduced Cardiac Risk for Breast Cancer Survivors

Abstract & Commentary

Synopsis: Women who survive breast cancer may be at a lower risk of developing coronary artery disease compared with women without a history of breast cancer. In this population-level cohort study, Lamont and colleagues from the University of Chicago analyzed data from the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) Medicare program to study the cardiac risk of elderly female Medicare beneficiaries with or without a history of breast cancer. They found that the risk for hospitalization for acute myocardial infarction was reduced significantly (34%) among the breast cancer survivors. Lamont et al speculate that, among other possibilities, the protective effect of prior breast cancer upon the development of acute myocardial infarction may be due to the use of selective estrogen response modifiers (SERMS) for the treatment of the breast cancer.

Source: Lamont EB, et al. Cancer. 2003;98:2-10.

Estrogen is strongly associated with both health and disease in women. Comparatively high estrogen exposure is protective against some diseases (eg, coronary heart disease and osteoporosis) but contributory to others (eg, breast and endometrial carcinoma). Recently, Lamont and associates from the University of Chicago have demonstrated that breast cancer survivors have reduced rates of osteoporosis (this manuscript is currently in press). In the current report, an examination of coronary artery disease as manifest by acute myocardial infarction was undertaken in postmenopausal women who have survived breast cancer. The report details an investigation of the National Cancer Institutes Surveillance, Epidemiology and End Results (SEER) Medicare Program. Elderly women survivors of stage 0, I, or II breast carcinoma (n = 5980) diagnosed between the ages of 55 and 64 were compared with age-matched women without a history of cancer (n = 23165) derived using the Medicare 5% Noncancer File. In addition to age, Lamont et al controlled the analyses for race, socioeconomic status, geographic location, cohort entry year, and medical comorbidity.

The hazard of hospitalization for acute myocardial infarction (AMI) for breast cancer survivors relative to the comparison group was 0.66 (95% CI, 0.49-0.88). The apparent cardioprotective effect was stronger in breast cancer survivors with documented cardiac risk factors. Lamont et al conclude that survivors of early stage, postmenopausal breast cancer are at significantly lower risk of hospitalization for acute myocardial infarction than women who do not have a history of breast cancer. Lamont et al call for further investigation into the mechanisms of this cardioprotective effect.

Comment by William B. Ershler, MD

This is a very interesting observation that may have public health implications. Lamont et al have identified a subset of women who have a 34% reduction in the disease that accounts by far for the largest numbers of deaths in elderly women in the United States. If additional work identifies the mechanism behind this reduction in cardiac risk in breast cancer survivors, the finding may be applicable to the cardiovascular health of the general population.

Three possible explanations come to mind. First, breast cancer survivors by virtue of the rigors of intensive surgical and medical management may be more health conscious and modify those controllable factors relevant to the development of coronary artery disease and acute myocardial infarction (eg, smoking, diet, etc). However, Lamont et al suggest that this explanation is less likely because their data demonstrated that hospitalization rates for other illnesses (eg, pneumonia) were not different in the 2 cohorts. Secondly, estrogens may be etiologic in the development of breast cancer yet protective in atherosclerosis, particularly coronary artery disease. Or, thirdly, a common therapy for breast carcinoma (eg, tamoxifen) may be associated with cardiac protection. Neither the SEER records nor the claims data would allow an accurate estimation of lifetime estrogen exposure or tamoxifen use, and therefore, although quite possibly the case, this association could not be satisfactorily addressed using the resources available. Additional research focused on mechanisms to explain this cardioprotective phenomenon would require data enriched with clinical variables such as tamoxifen use and the influence thereon of certain cardiac risk factors.

Despite the constraints and inherent problems of exploring claims data, the findings that elderly women with a history of postmenopausal breast cancer have a 34% lower hazard of hospitalization for acute myocardial infarction is of great interest. It is quite possible that the cardiac protection relates to the use of SERM’s and, therefore, the data may have public health implications for women without a history of breast cancer. Further evaluation to define the mechanisms of this cardioprotective effect is warranted.

Dr. Ershler is UNOVA Fairfax Hospital Cancer Center, Fairfax, VA; Director, Institute for Advanced Studies in Aging, Washington, D.C.