European researchers found that radiation therapy given at any dosage for breast cancer increases a woman’s risk of heart disease, with higher doses leading to higher rates of risk.
Though there did not seem to be a dose at which the heart was unaffected, the study assessed women receiving radiation therapy more than a decade ago, some of whom received higher doses than are recommended today. Today’s techniques, including deep inspiration breath hold, better protect the heart.
The authors of the study say the benefits of treating breast cancer with radiation outweigh potential harm to the heart.
Past studies have shown that radiation therapy for breast cancer is related to the risk of developing heart disease. The closeness of the heart to the breasts means some radiation exposure to it cannot be avoided. However, little is known about the effect of doses on risk, or how long after radiation it may take for heart problems to start.
The researchers sought answers to these questions by comparing individual women’s instances of heart disease to the estimated dose of radiation they received during treatment for breast cancer. They also considered whether each woman who had a pre-existing heart problem was at greater risk of developing one because of other health or lifestyle factors, such as being overweight or smoking.
Information on the women’s radiation therapy, past medical history and tumor characteristics was taken from 2,168 treatment records in the Swedish National Cancer Register and Danish Breast Cancer Cooperative Group register. In the Swedish group, all women selected were diagnosed between 1958 and 2001, were younger than 70 at diagnosis, and had radiation therapy. In the Danish group, women were diagnosed between 1977 and 2000, were younger than 75 at diagnosis, and had radiation therapy.
Major coronary events were defined by the investigators as a heart attack, treatment to help bring oxygen to the heart, or death from heart disease.
In total, 936 women who had a major coronary event after radiation treatment for breast cancer, but before recurrence or a second cancer diagnosis, were compared with 1,205 women who had radiation treatment but did not have any heart problems.
The results showed all women treated with radiation therapy have greater risk of developing heart problems, even when the dose is small. Though the risk is low at lower doses, the higher the dose the greater the risk – for each unit of radiation used, a woman’s risk increased by 7.4 percent.
The time to the start of heart problems varied, but overall the data showed that the risk of major coronary events increased within 5 years of treatment, and lasted at least 20 years. Of the women in this study who had a heart problem
- 44 percent occurred less than 10 years after diagnosis
- 33 percent occurred 10 – 19 years after diagnosis
- 23 percent occurred more than 20 years after diagnosis
Women who were treated for breast cancer in the left breast, over theheart, had higher rates of heart problems than women treated in the right breast.
What This Means for You
Though these findings show that the risk of heart problems is higher after radiation therapy, radiation is still a very important part of treatment for many breast cancers. Research has shown radiation greatly reduces the risk of recurrence and improves long-term survival.
It is important to know that this study did not include many women under age 40 nor many women treated with anthracycline- or taxane-based chemotherapy or trastuzumab (Herceptin), all of which can cause heart-related side effects. If you are under 40 or received these treatments and are concerned about your heart health, talk with your doctor.
When discussing treatment with your healthcare team, ask your doctors how they will limit your risks, and tell them about any lifestyle factors that may increase your chance of developing heart problems. Your doctors will help you choose the best treatment plan.
Darby, SC, Ewertz, M, McGale, P, et al. Risk of ischemic heart disease in women after radiotherapy for breast cancer. New England Journal of Medicine. 2013;368: 987-998.