TUESDAY, Dec. 27, 2011 (HealthDay News) -- Women who have breast cancer on the left side of the body and who are treated with radiation therapy have a higher risk of developing narrowing of the arteries that lead to the heart, researchers say.
A new Swedish study found that the risk of having moderately narrowed coronary arteries was more than four times greater for women who had left-sided breast cancers treated with radiation compared to right-sided breast cancers treated with radiation. The odds were seven times higher for more severe narrowing on the left side versus the right, according to the study published in the Dec. 27 online edition of the Journal of Clinical Oncology.
"We suggest that the coronary arteries be regarded as organs at risk in radiation therapy, and that every effort be made to avoid radiation dose to the coronary arteries," wrote study authors led by Dr. Greger Nilsson, of the department of oncology, radiology and clinical immunology at Uppsala University Hospital.
However, it's also important to note that of a group of 8,190 women who had breast cancer, just 199 had to be referred for coronary angiography (a treatment for blocked blood vessels).
"Women need to be aware that there is a risk, but the overall risk is still relatively small, and the benefits of radiation in the treatment of breast cancer still outweigh the risks," said Dr. Stephanie Bernik, chief of surgical oncology at Lenox Hill Hospital in New York City.
Cancer treatments, such as radiation and chemotherapy, are designed to destroy cancer cells. Unfortunately, healthy cells are often damaged, too. Treatment techniques are constantly being refined, and today's treatments target fewer healthy cells than treatments from years past.
For example, newer radiation techniques help protect the heart and the arteries leading to it, according to Dr. Timothy Zagar, an assistant professor in radiation oncology at the University of North Carolina at Chapel Hill. One such technique is to give bursts of radiation only when a patient is taking a deep breath. During a deep breath, the main artery going to the heart separates from the breast and chest wall, which keeps it away from the radiation.
Zagar, co-author of an accompanying editorial in the same issue of the journal, said researchers don't know exactly how radiation causes damage to coronary arteries, but it's believed to damage the cells lining the arteries (endothelial cells), which causes inflammation, which can lead to hardening of the arteries.
The current study included women from Sweden who were diagnosed with breast cancer between 1970 and 2003. Of the 8,190 women, the researchers found 199 women who had undergone coronary angiography, suggesting significant coronary artery disease.
Coronary artery narrowing (stenosis) is graded on a scale of zero to 5. Zero indicates a healthy blood vessel, while 5 indicates a blocked blood vessel.
When the researchers compared women who'd had radiation treatment on the left side of their body versus the right, they found that the odds of a grade 3 to grade 5 stenosis in a left-sided artery were 4.38 times higher. The odds of a grade 4 or grade 5 stenosis were 7.22 times higher for women who had left-sided breast cancer.
In women who received radiation in high-risk areas near the heart's arteries, the risk of a grade 3 to grade 5 stenosis was nearly twice as high as it was in women who had radiation in low-risk areas, or who didn't have radiation.
Zagar pointed out that this study was done over a long period of time and that changes in the way radiation is delivered would likely result in lower odds of coronary artery stenosis for women treated with radiation today.
In addition, Zagar said, "I don't think this study's findings would justify changing from a lumpectomy [breast-conserving surgery] to a mastectomy [surgical removal of the breast]. Breast-conserving therapy is very important to many women, and the number of coronary events are still low," he added.
"It's important to understand that with all treatments, there are risks," Bernik said. "And, we know that this is one of the risks with radiation of left-sided breast cancer. Women need to keep in mind that they're at increased risk of coronary events and need to follow up with their doctor going forward."
Learn more about radiation treatment for cancer from the U.S. National Cancer Institute.