Breast cancer, radiation therapy and heart disease: the risks

These days, thanks to advances in treatment and detection, millions of women survive breast cancer. But surviving the disease doesn’t necessarily mean the entire battle is over, a population-based study of breast cancer survivors in Sweden and Denmark, published Wednesday in the New England Journal of Medicine, seems to suggest.

Assessing a total of 2,168 women whose breast cancer was treated with radiation therapy between 1958 and 2001, a team of researchers found that women’s chances of having a major coronary event — a heart attack, bypass surgery or heart disease death — rose in proportion with the radiation dose they received, even at the lower doses of radiation delivered in newer treatments.

In all, 963 of the women in the study had major coronary events.

Forty-four percent of these took place within 10 years of the cancer diagnosis, but 33% occurred 10 to 19 years later, and 23% occurred 20 or more years later. Estimating the amount of radiation the women had received to their hearts over the course of their breast cancer treatment, the researchers also calculated that the rate of major coronary events increased 7.4% per gray (a unit of absorbed dose) of radiation.

Women with cancers in the left breast, which is closer to the heart, had higher rates of coronary events than women treated for tumors in the right breast.

Patients who had other risk factors for cardiovascular disease — those who had a high body-mass index, smoked or had diabetes, as well as other factors — had higher rates of serious heart problems than women with lower underlying risks.

Writing in an editorial that accompanied the study, Dr. Javid Moslehi, co-director of the Cardio-Oncology Program at Brigham and Women’s Hospital in Boston, argued that the findings should bolster efforts to offer cancer patients specialized cardiac treatment as they battle their disease.

He also suggested that the breast cancer-radiotherapy study might represent merely “the tip of the iceberg” — that exposure to radiation might also increase risks of conditions like pericardial disease and arrhythmias. Cancer treatments beyond radiation therapy might also increase heart disease risk, he said.

“The current study calls for greater collaboration between oncologists and cardiologists,” he wrote. “The time to address concerns about cardiovascular ‘survivorship’ is at the time of cancer diagnosis and before treatment rather than after completion of therapy.”

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