Most of the nearly 300,000 American women diagnosed with breast cancer each year receive radiation to help prevent a relapse, yet a new study suggests that those treatments increase the risk of heart attacks and of dying from heart disease up to 20 years later.
The findings, published Wednesday in the New England Journal of Medicine, emphasize the need for better cardiac care for breast cancer survivors, many of whom also take chemotherapy drugs that weaken their heart muscle.
“Breast cancer patients who are candidates for radiation should still receive radiation,’’ said study co-author Dr. Candace Correa, a radiation oncologist at the H. Lee Moffitt Cancer Center and Research Institute in Tampa, Florida. “This isn’t an alarmist study, but should be used to estimate radiation risks to the heart and take efforts to reduce that dose.’’
The European and American researchers examined medical records from nearly 1,000 Danish and Swedish breast cancer patients who developed heart disease or died from it after they were treated with radiation for breast cancer during the period of 1958 to 2001. They found that for each 1 gray (Gy) dose of radiation delivered to the heart, women had a 7.4 percent increased risk of heart disease.
While those with heart disease risk factors like diabetes or high blood pressure had the greatest likelihood of having heart problems after radiation, the researchers found that radiation was associated with an elevated heart risk even in those without any other risk factors. They calculated that a 50-year-old woman without any heart risk factors who had a radiation dose of 3 Gy to her heart increased her risk of dying from heart disease before age 80 from 1.9 percent to 2.4 percent and her risk of having a heart attack from 4.5 percent to 5.4 percent.
Women treated with radiation for tumors in their left breast, near the heart, received an average dose of nearly 7 Gy of radiation to their heart. Women with tumors in their right breast had an average dose of about 3 Gy.
“I think these findings are just the tip of the iceberg,’’ said Dr. Javid Moslehi, co-director of the cardio-oncology program at the Dana-Farber Cancer Institute, who wrote an editorial that accompanied the study. “Radiation can cause other diseases associated with the heart such as arrhythmias, valve problems, and vascular disease linked to strokes, which the study didn’t measure.’’
The study excluded women who took potent chemotherapy drugs known to damage the heart; many breast cancer patients with invasive tumors that have spread to the lymph nodes undergo radiation along with those drugs, which likely increases their heart risks even further.
Other oncologists, however, caution that the study findings may not apply to modern radiation treatments for breast cancer, which deliver lower doses using more targeted methods to minimize exposure to the heart. For example, women may be told to inhale and hold their breath while being zapped to nudge the heart out of the way, which has been shown to work in recent studies.
“I’m worried that women will read about these findings and decide that they don’t want to get breast-conserving surgery because they’re worried about the heart risks from the radiation,’’ said Dr. Mehra Golshan, director of breast surgical services at Dana-Farber/Brigham and Women’s Cancer Center, who wasn’t involved in the study.
The new research does not justify that reaction, he added, because previous studies have shown no survival difference between breast cancer patients who choose to have a mastectomy to remove their early stage breast cancer compared to those who have breast-conserving surgery with radiation.
Radiation therapy is crucial for those who opt for lumpectomies to prevent recurrences in the breast tissue, surrounding chest wall, and nearby lymph nodes that can go on to spread and kill. Some women with more advanced cancers might also need radiation along with a mastectomy for the same reason.
What’s not known, however, is whether women with tiny self-contained cancers — called ductal carcinoma in situ — face a greater risk of recurrence if they have breast-conserving surgery without the radiation. As of now, they usually get the two in combination, but researchers are trying to determine whether some women with these small cancers can safely skip the radiation, and its heart risks, even if they opt not to have a mastectomy.
For the millions of breast cancer survivors treated with radiation years or decades ago, Moslehi said the study underscores the importance of follow-up with a cardiologist at some point after treatment to ensure that no damage has been done to the heart muscle.
“Radiation treatment for breast cancer should be considered a risk factor for heart disease along with other known risk factors, like high cholesterol and high blood pressure,’’ he said. “And patients should be more aggressive in keeping these other risk factors under control with medication and lifestyle changes if they had radiation or certain chemotherapy drugs.’’