More than 16 percent of women who did not survive after being diagnosed with early-stage breast cancer died from cardiovascular disease, according to a population-based cohort study.

Lead researcher Husam Abdel-Qadir, MD, of the University of Toronto, and colleagues published their results online in JAMA Cardiology on Oct. 12.

The researchers evaluated the Ontario Cancer Registry and identified nearly 99,000 women who were diagnosed with early-stage breast cancer between April 1, 1998, and March 31, 2012. The median age was 60 years old, and 37.8 percent of the women were at least 66 years old when they were diagnosed. In addition, 6.6 percent of the women had previous cardiovascular disease.

The women were followed up until they died or until Dec. 31, 2013, whichever came first.

During a median follow-up period of 6.6 years, 21.3 percent of the women died. The median time to death was 4.2 years. The most common causes of death were breast cancer (49.9 percent of deaths) and cardiovascular causes (16.3 percent of deaths).

The researchers said that cardiovascular death was uncommon in women who were younger than 66 years old and had no prior cardiovascular disease, diabetes or hypertension. However, among women who were at least 66, the risk of breast cancer death at 10 years was 11.9 percent and the risk of cardiovascular death at 10 years was 7.6 percent.

Women who were at least 66 years old at diagnosis accounted for 89.6 percent of cardiovascular deaths and 43.9 percent of breast cancer deaths.

Among the patients with a history of cardiovascular disease, the risk of death from breast cancer and cardiovascular disease was similar during the first five years. However, beyond five years, the risk of death from cardiovascular causes was higher.

“Although management of breast cancer should be the primary focus of women with [early-stage breast cancer], our data highlight the importance of competing risks,” the researchers wrote. “Women with [early-stage breast cancer] are just as likely to die from causes other than breast cancer, chief among which is cardiovascular disease. Given the effectiveness of both primary and secondary prevention interventions for cardiovascular disease, appropriate care for women with [early-stage breast cancer] should involve counseling and preventive interventions that are proportionate to their expected cardiovascular risk.”

The researchers acknowledged potential limitations of the study, including that they did not assess risk factors such as dyslipidemia and smoking. They also relied on death certificate data, which might not always be accurate. In addition, they could not detect death in women who left Ontario.

“Our results highlight that age and previous history of cardiovascular disease are strong predictors of cardiovascular risk in women with [early-stage breast cancer],” they wrote. “These traditional risk factors can serve as an inexpensive initial screening tool to identify women who could most benefit from preventive interventions. ... Appropriate risk stratification can identify women with [early-stage breast cancer] who could benefit from cardiovascular disease prevention strategies. Further research on cardiovascular disease in women with breast cancer is warranted.”