MORTALITY FROM MYOCARDIAL-INFARCTION AFTER ADJUVANT RADIOTHERAPY FOR BREAST-CANCER IN THE SURVEILLANCE, EPIDEMIOLOGY, AND END-RESULTS CANCER REGISTRIES

Purpose: To compare the risk for fatal myocardial infarction (MI) afte r adjuvant radiotherapy (RT) for left-sided breast cancer with the ris k for MI after adjuvant RT for right-sided breast cancer. Methods: We studied women with local- and regional-stage breast cancer diagnosed f rom 1973 to 1992 from the Surveillance, Epidemiology, and End-Results (SEER) cancer registries, We performed life-table analysis, the log-ra nk test, and Cox proportional hazards regression to compare the time t o fatal MI from diagnosis between left-sided and right-sided cases, ce nsoring deaths from other causes. Results: Among irradiated patients, the relative risk (RR) for fatal MI in women with left-sided breast ca ncer was 1.17 (95% confidence interval [CI], 1.01 to 1.36), controllin g for age, compared with those with right-sided breast cancer. The RR for fatal MI among left-sided cases was increased for those under the age of 60 years (RR = 1.98; 95% CI, 1.31 to 2.97) compared with right- sided cases, but not at age 60 years or older. Among women with irradi ated regional-stage cancer who were younger than 60 years of age, the risk was significantly increased (RR = 2.24; 95% CI, 1.38 to 3.64) for those wish left-sided compared with right-sided breast cancer, but no t among patients aged 60 years or older. Among irradiated local-stage cases, the risk for those with left-sided breast cancer was not signif icant ly elevated in either age category. Analysis of 5-year condition al survival cohorts showed an increased risk for irradiated left-sided cases among women younger than 60 years of age in the 10- to 15-year conditional survival cohort (RR = 5.28; 95% CI, 1.82 to 15.3). Conclus ion: Adjuvant RT for left-sided breast cancer diagnosed in women young er than 60 years of age is associated with a higher risk for fatal MI 10 to 15 years later compared with adjuvant Ri for right-sided cases. J Clin Oncol 16:2625-2631, (C) 1998 by American Society of Clinical On cology.