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 surge
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