Women treated for breast cancer with radiation therapy are more likely to die from heart disease 20 years or more down the line than women who don’t get radiation, according to a new study.

Previous studies have suggested that radiation close to the heart can increase a woman’s risk of getting heart or blood vessel-related disease in the future - but little is known about how that risk plays out over multiple decades. The results are from women who received radiation in the 1980’s and earlier, when doses of radiation were significantly higher than those used today.

Radiation “is a very important part of therapy for many women,” Dr. Ronald Witteles, who studies heart disease at Stanford University and wrote an editorial accompanying the current study, told Reuters Health.

However, “we need to honestly look at the risks and take them into account when making treatment decisions,” he said.

The researchers, led by Dr. Kim Bouillon of the Gustave Roussy Institute in France, tracked 4,456 women who had been treated for breast cancer at the Institute between 1954 and 1984. About two-thirds of the women received radiation therapy during their treatment.

Using a national database of all deaths starting in 1972, the authors were able to determine which women had died - and of what - and which were still alive as of 2003. Because they were interested only in the long-term effects of radiation, the authors did not include in the study any women who died within 5 years of being treated.

In the 30 years following breast cancer treatment, women who had received radiation treatment were no more likely to die from heart disease or stroke than women who didn’t get radiation. By the end of the study period, between 5 and 6 percent of women in both groups had died of heart disease, and between 8 and 11 percent had died of any kind of heart disease or stroke.

However, when the researchers took into account the age at which women died, women who had been treated with radiation died from heart disease at between one and a half and two times the rate of women who hadn’t been treated with radiation. Age of death is important because the effects of radiation on the heart are thought to take 10 to 20 years to show up, in some cases.

In that same analysis, women who had been treated with radiation on their left breast - where it’s harder to avoid radiation to the heart - were more likely to die of heart disease than women who had radiation therapy on the right breast, 20 years after their treatment procedures.

Because of the nature of the study, the authors were not able to prove that radiation caused heart disease.

It’s possible that the cardiovascular effects of radiation will not be a problem for women being treated with radiation therapy in the present, as current radiation levels used in treatment are much lower than they were 30 years ago. But researchers won’t know the long-term consequences of radiation as it is used today for another couple of decades - making it difficult for doctors and patients alike to make informed treatment choices.

“One has to believe that the less radiation that is delivered to the heart, the less cardiovascular effect you’ll see,” Witteles said. But, he added, “Radiation injury to the heart simply doesn’t manifest itself as a problem until at least 10 years later.”

And radiation therapy may have very different impacts on different women, Witteles said. “There’s still great variation both in terms of what part of the heart is getting radiation and how radiation is being given individual to individual, because it depends a lot on their anatomy,” he said.

Based on that anatomy - such as the location of the tumor in relation to the heart - doctors who perform radiation usually have a pretty good idea of how much radiation the heart will be exposed to, Witteles said. That factor should be a part of treatment discussions between women and their doctors, he said.

If the risk of radiation to the heart is high, some women may choose to get a mastectomy, which doesn’t require radiation treatment.

“There is a common misconception that because of advancements in radiation techniques this is almost a non-issue,” Witteles said. However, even now, the possible risk to the heart “needs to be taken into account when deciding between different treatment options,” he said.

SOURCE:  Journal of the American College of Cardiology, January 25, 2011.