March 15, 2013
Breast Cancer Radiotherapy Raises Risk Of Heart Disease Slightly
April Flowers for redOrbit.com - Your Universe Online
Doctors have known for quite a while that radiation treatment for breast cancer increases a woman's risk of heart disease, but the extent of that additional risk was unknown. A new study, published in a recent online issue of The New England Journal of Medicine (NEJM), further explains those risks.
The New York Times reports that a new study led by the University of Oxford's Clinical Trial Service Unit (CTSU) offers a way to estimate the risk. The study finds the risk is modest for most women and is outweighed by the benefit from the treatment. For breast cancer, radiation can halve the recurrence rate and lower the death rate by about one-sixth.
For example, a 50-year-old woman with no prior cardiovascular risks has a 1.9 percent chance of dying of heart disease before her 80th birthday. That risk increases to between 2.4 and 3.4 percent with radiation therapy for breast cancer, depending on how much radiation hits the heart.
“It would be a real tragedy if this put women off having radiotherapy for breast cancer,” said Sarah Darby, a professor of medical statistics at the University of Oxford.
The chairwoman of radiation oncology at New York University (NYU) Langone Medical Center, Dr. Silvia Formenti, worries that women with cancer will misconstrue the findings and avoid radiation for breast cancer, choosing instead to have a full mastectomy instead of a lumpectomy.
“There is a wave toward mastectomy in this country,” Dr. Formenti said. She does confirm, however, that the cardiovascular risk is real and every effort to minimize exposure of the heart should be taken.
The experts also warn that women given radiation therapy for breast cancer should be especially vigilant about controlling other factors that might increase the odds of heart disease, such as high blood pressure and cholesterol.
The researchers examined 2,1268 breast cancer patients in Sweden and Denmark who underwent radiation therapy between 1958 and 2001. According to USA Today, the doctors found that any amount of radiation increased the risk of heart disease, which they defined to include heart attacks, surgeries such as a bypass or angioplasty, or a heart-related death.
“It was certainly a surprise to us that the risk started within the first few years after exposure, as radiation-related heart disease has traditionally been thought of as usually occurring several decades after exposure,” Dr. Darby said.
"This is a major concern," says Ben Smith, an assistant professor of radiation oncology at M.D. Anderson Cancer Center in Houston, who was not involved in the new study. In spite of improvements in technology, Smith says many women around the country "still have a significant portion of their heart in the path of the radiation beam."
The study reveals that women who received radiation to the left breast were at an especially higher risk as that breast is closer to the heart. Women with pre-existing heart disease were at a higher risk as well. The study showed that heart problems most commonly appeared in the first five to ten years after treatment.
Each additional unit of radiation, called a gray, increased the risk of heart disease an average of 7.4 percent over 20 years. The average dose of radiation to the heart for women in the study was 4.9 gray, although some women received as much as 27 gray.
Even though doctors have worked to reduce unnecessary radiation exposure over the years, American women being treated today may still receive 2 to5 gray to the heart. Smith says that new technology available at his hospital allows doctors to reduce that exposure to a fraction of 1 gray.
NEW WAYS TO REDUCE EXPOSURE
The more common dosage is 2 gray, according to Dr. Louis S. Constine, vice chairman of radiation oncology at the University of Rochester Medical Center. Dr. Constine says that doctors can now shield the heart and “curve radiation around the chest wall instead of shooting it through the heart and lungs.”
The best way to protect the heart for most patients, Dr. Formenti thinks, is to treat them while they are lying on their stomachs, instead of on their backs as usual. With the new method, women would lie on their stomachs on a table or mattress with openings that allow the breasts to drop away from the chest. This position, even though individual anatomy differs, would keep radiation beams as far from the heart and lungs as possible. The radiation dosage received by the heart is much less, especially when the left breast is treated.
“If you can keep it below 1 Gray, which is what we are doing, you are probably O.K. with the majority of patients,” Dr. Formenti said.
At M.D. Anderson in Houston, Texas, women receive radiation therapy that is synchronized with their breathing. Inhaling deeply, Smith says, pushes the heart down and out of the radiation beam. The beam is started and stopped automatically as women breathe in and out, almost eliminating exposure to the heart.
According to Smith, approximately 60,000 women a year are diagnosed with a condition called DCIS, or ductal carcinoma in situe. Although not all the tumors are life-threatening, about 30 to 40 percent of DCIS progresses into invasive cancer. The uncertainty leads to treatments for early cancer, with a lumpectomy, radiation and sometimes hormone therapy.
"Any concerns about radiation become an even bigger issue for women who have very early stage breast cancers like DCIS, where women have to very carefully weight the pros and cons of treatments," Eric Winer, director of breast medical oncology at Dana-Farber says. "We need to figure out which women with DCIS need treatment to spare women from the side effects."
This research is the first to provide risk estimates correlated with doses in breast cancer treatment, over a long period, said Dr. Javid Moslehi, co-director of the cardio-oncology program at the Dana-Farber Cancer Institute in Boston. Dr. Moleshi says the study reflects the fact that many people with cancer are living long enough to encounter long-term effects of both radiation and chemotherapy.
“This is a huge paper, both in terms of how many women it impacts, and how it opens the door for new studies that need to be done,” Dr. Moslehi said. Dr. Molslehi believes this paper may "represent just the tip of the iceberg" because radiation can cause not just narrowing of the arteries and heart attacks, but abnormal heart rhythms, malfunctioning heart valves and other serious issues, which weren't measured in this study.
According to Moslehi, certain chemotherapy drugs can also damage the heart as well as throw women into early menopause. Early menopause, says Jody Schoger, a breast cancer survivor and advocate from The Woodlands, Texas, causes breast cancer survivors to gain weight, putting further stress on the heart.
There is some disagreement about the validity of the study, however.
The findings mean a history of breast irradiation should be added to the list of risk factors for heart disease, said Dr. Lori Mosca, the director of preventive cardiology at New York-Presbyterian Hospital/Columbia University Medical Center. This should be taken into consideration by all doctors who are treating such patients.
“We absolutely need to put on our radar screen that prior radiation to the breast may be a new and important risk factor for women,” Dr. Mosca said. She and other experts, however, warn that the results need to be verified because the study was not a controlled experiment. Instead, it was an analysis of records and estimates of radiation exposure.