Radiation therapy for left-sided breast cancer linked to elevated CV risk
Women with left-sided breast cancer treated with radiation therapy have a greater risk for developing narrowing of the arteries that lead to the heart, according to a study published online in the Journal of Clinical Oncology.
A Swedish cohort study of 8,190 patients diagnosed with invasive breast cancer or ductal carcinoma in situ from 1970 to 2003 yielded 199 women who also received coronary angiography from 1990 to 2004. Under review by radiologists, coronary arteries — including right coronary artery (RCA), left main coronary artery, left anterior descending artery (LAD) and left circumflex artery — were divided into 18 segments and graded according to a five-grade scale of stenosis, in which zero indicated a normal vessel and five indicated occlusion of the vessel.
Before analysis, the two areas determined most likely to receive radiation dose were segments located to the left of the sternum — including the mid, distal and distal diagonal branch of the LAD (mdLAD + dD) — and segments located retrosternal, close to the midline in the superior part and then running inferior to the right of the sternum, parallel to the proximal RCA.
To account for varying radiation therapy regimens, radiation dosage and risk for radiation to coronary arteries during the course of the study period, researchers categorized the radiation therapy targets and regimens as high or low risk, regarding the hotspot areas of proximal RCA and mdLAD + dD.
Left-sided radiation to the chest wall or breast was considered high risk for mdLAD + dD, whereas radiation delivered to the left internal mammary chain was deemed a high risk for both proximal RCA and mdLAD + dD. Radiation to the right internal mammary chain was marked as high risk for proximal RCA, but all remaining radiation targets — including right chest wall, right breast and axillas — were considered to be at low risk for receiving radiation.
Compared with patients with right-sided breast cancer, researchers found that those with left-sided breast cancer demonstrated an increased incidence of stenosis of all segments and all grades of stenosis. Patients with left-sided breast cancer also exhibited stenosis in mdLAD + dD and the OR increased with more severe stenosis.
Further dividing the left-sided vs. right-sided groups into irradiated and non-irradiated breast cancers, the study revealed a significant increase of stenosis in mdLAD + dD for irradiated breast cancers: grade 1 to 5 (OR=2.04; 95% CI, 1.18-3.55), grade 3 to 5 (OR=4.38; 95% CI, 1.64-11.7) and grade 4 to 5 (OR=7.22; 95% CI, 1.64-31.8). For proximal RCA, there were no statistically significant discrepancies for stenosis between irradiated left- and right-sided breast cancer.
Disclosure: The researchers report no relevant financial disclosures.
This very interesting retrospective analysis looks to link radiation exposure of coronary arteries during the course of radiation for breast cancer with subsequent coronary artery stenosis as judged by angiography. It is made possible by access to long-term follow-up data in a Swedish cohort. There are several limitations, including the evolution of radiotherapy techniques over the decades under study, as well as the lack of information about whether the findings have clinical consequences. It would be useful to know if other groups with similar data sets can replicate the findings. Nonetheless it is a sobering reminder that we must always be mindful about the potential for long-term side effects when treating early-stage breast cancer.
– Nancy Davidson, MD
Director, University of Pittsburgh Cancer Institute and UPMC Cancer Centers
Chief, Division of Hematology-Oncology
University of Pittsburgh Department of Medicine
Disclosure: Dr. Davidson reports no relevant financial disclosures.
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