Abstract P4-11-02: Increase of Coronary Artery Stenosis after Radiation for Breast Cancer
Authors: Nilsson G , Holmberg L , Garmo H , Duvernoy O , Sjögren I , Lagerqvist B , Blomqvist C. 
Published: April 2011

Abstract
Purpose: To study the distribution of coronary artery stenosis among breast cancer (BC) subjects; to assess any correlation between radiotherapy (RT) and the location of stenosis.
Methods: A population based Swedish BC cohort diagnosed 1970-2003 was linked to registers of coronary angiography 1990-2004 and yielded 199 subjects with BC followed by a coronary angiography. The right coronary artery (RCA), the left artery descendens (LAD), and the left circumflex artery, were divided into multiple segments according to the American Heart Association classification. The segments were graded 0-5, where grade 0 was a vessel without any stenosis, grade 1-4 increasing grade of stenosis, and grade 5 was occlusion. Stenoses with at least 70 % diameter narrowing (i.e. grade 3-5) were considered as clinically significant. Hotspot segments for exposure to radiation were defined a priori. RT targets and regimens were categorized as high risk or low risk, regarding radiation to these hotspot segments. Left breast/chest wall was considered high risk for segments 7+8+10 (mid and distal LAD). Due to the radiation technique, the left internal mammary chain (IMC) was regarded as high risk for segments 1+2 (proximal RCA) and 7+8+10 during 1970-1994, and thereafter only for segments 7+8+10. Right IMC was deemed high risk for segments 1+2. Other RT targets and no RT were considered low risk. When comparing left sided BC to right sided, we used conditional logistic regression. In the analysis of hot spot segments, a generalized linear mixed model was used. Associations between RT and coronary artery stenosis were expressed as odds ratios (OR) and 95 % confidence intervals (CI).
Results: Mean age at diagnosis of BC was 58.2 years (yr) and left sided BC was slightly more common than right sided, 55 % vs. 45 %. Median follow-up period between BC and coronary angiography was 10.3 yr. The majority of the women with BC had low risk disease, T1-2N0. Sixty-two percent (123/199) of the BC subjects received RT and twenty-nine percent (58/199) were irradiated to the IMC. Adjuvant chemotherapy and endocrine therapy was seldom used, only received by 9 % and 17 % of the subjects, respectively. For left vs. right sided BC, the OR for grade 1-5 stenosis in segments 7+8+10 was 1.44 (CI = 0.95-2.18), grade 3-5 (OR = 2.18; CI = 1.16-4.09), and grade 4-5 (OR = 2.91; CI = 1.24-6.83). When restricting the comparison to left vs. right sided RT treated BC, larger differences emerged. The OR for grade 1-5 stenosis in segments 7+8+10 was 2.04 (CI = 1.18-3.55), grade 3-5 (OR = 4.38; CI = 1.64-11.7), and grade 4-5 (OR = 7.22; CI = 1.64-31.8). For high risk RT vs. low risk, the OR for grade 1-5 stenosis in the hotspot segments was 1.85 (CI = 1.17-2.93), grade 2-5 (OR = 1.33; CI = 0.83-2.13), and grade 3-5 (OR = 1.90; CI = 1.11-3.24). Conclusion: We found a clear and statistically significant increase of coronary artery stenosis in the mid and distal LAD among irradiated left sided breast cancer and an association between RT targets a priori defined as high risk for cardiac exposure and coronary stenosis in hotspot segments for radiation. We found no other plausible explanation than the target area for the RT. Our results therefore suggest that effort should be made to avoid radiation dose to the coronary arteries.
Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P4-11-02.