A 2016 study compared the risks of dying from breast cancer and cardiovascular disease in women diagnosed with early-stage breast cancer. The risk of cardiovascular disease was decreased in women under the age of 66 and greatly increased in women 66 and above, though breast cancer was the leading cause of death in patients under 66.
It is difficult to determine the risk of dying from breast cancer compared to cardiovascular disease for women diagnosed with early-stage breast cancer (EBC). Beyond the overlap between their risk factors, a number of breast cancer therapies are associated with adverse cardiovascular events. A better understanding of the risk of mortality for both conditions would inform decisions concerning the treatment of women diagnosed with early-stage breast cancer.
A 2016 study published in JAMA Cardiology compared the likelihoods of dying from breast cancer and cardiovascular disease in women diagnosed with EBC. Patient data was obtained from the Ontario Cancer Registry. The study included all women diagnosed with EBC between April 1, 1998, and March 31, 2012, who were eligible for the Ontario Health Insurance Plan, were younger than 105 years of age, and for whom information on their age and diagnosis date were available. Age-matched controls – women without an EBC diagnosis – were chosen under the same criteria.
For women under 66 years of age, the cause of death was categorized as due to breast cancer, cardiovascular disease, other cancers, or other non-cancer causes. For women 66 years and above, the non-cancer category was further divided into four: dementia or brain degeneration; pneumonia, blood or tissue infections, or urinary tract infections; diabetes; and other causes. Risk was assessed with respect to a number of factors: age, below 66 or 66 and over; prior cardiovascular disease, including heart attacks, congestive heart failure, heart valve disease, conditions which affect circulation in the brain, and surgery to redirect or re-establish blood flow; and current cardiovascular disease, diabetes, or high blood pressure. With respect to baseline cardiovascular risk, age was also categorized as 55 and under, 56-66, 66-75, or over 75. Further analyses were conducted for women who survived five years or more after their diagnosis with EBC.
Data from 98,999 women with EBC was collected. The median age of subjects was 60, with 37,425 (37.8%) aged 66 and over. In total, 6,559 (6.6%), with a median age of 77, had prior cardiovascular disease, while 42,724 (43.2%) were below 66, had no prior cardiovascular disease and did not have diabetes or high blood pressure. Regarding treatment, a total of 44,675 (45.1%) women received chemotherapy, 45,592 (46.1%) received radiation therapy, and 7,851 (7.9%) received cancer immunotherapy with trastuzumab. Of the women 66 years and older, 11,094 (29.6%) and 13,331 (35.6%) respectively received aromatase inhibitors and tamoxifen, drugs which limit the action of estrogen.
The median length of follow-up was 6.6 years, with 26,752 (27%) having more than 10 years of follow-up. In total, 21,123 (21.3%) died during follow-up, with a median time to death of 4.2 years. Breast cancer was the most common cause of death at 10,550 incidents, comprising 10.7% of the EBC group and 49.9% of all deaths. Cardiovascular disease followed at 3,444 incidents, comprising 3.5% of the EBC group and 16.3% of all deaths. Women 66 and older accounted for 3,087 incidents (89.6%) of cardiovascular deaths and 4,629 incidents (43.9%) of breast cancer deaths. In the control group, the incidence of death due to breast cancer was less than 0.1%. Those in the EBC group were less likely to die from non-breast cancer conditions than were controls. For example, the rate of cardiovascular death at 10 years of follow-up was 3.2% for the EBC group and 4.4% for the control group. Of participants with a history of cardiovascular disease, the rate of death from cardiovascular disease and breast cancer were similar for the first five years (12.6% and 12.4%, respectively), beyond which the incidence of cardiovascular disease overtook that of breast cancer (16.9% and 14.6% at 10 years). Women in the EBC group under 66 without a history of cardiovascular disease, and without diabetes or high blood pressure, saw almost no cardiovascular disease-related death (0.5%).
Age was found to have the greatest impact on cardiovascular death risk. Women in the EBC group over 66 were 10.42 times as likely to die from cardiovascular complications as their younger counterparts. Moreover, women over 75 had 42 times the cardiovascular risk as those 55 and below. Breast cancer was the most frequent cause of death among younger women.
The results of this study suggest age plays an important role in the risk of dying from breast cancer compared to cardiovascular disease for women diagnosed with early-stage breast cancer. It should be noted that other important risk factors for breast cancer and cardiovascular disease, such as smoking or high cholesterol, were not taken into account in the analysis. With respect to treatment, therapies with known adverse effects on cardiovascular health, such as aromatase inhibitors and tamoxifen, may, therefore, prove unsafe for EBC patients above the age of 66, and above 75 in particular, and for patients with a history of cardiovascular disease treated beyond 5 years. Further research may be required to determine to what extent such drugs impact cardiovascular risk with respect to age.
Written By: Raishard Haynes, MBS