Mortality from myocardial infarction after adjuvant radiotherapy for breast cancer in the surveillance, epidemiology, and end-results cancer registries.
OBJECTIVE
To compare the risk for fatal myocardial infarction (MI) after adjuvant radiotherapy (RT) for left-sided breast cancer with the risk for MI after adjuvant RT for right-sided breast cancer.


METHODS
We studied women with local- and regional-stage breast cancer diagnosed from 1973 to 1992 from the Surveillance, Epidemiology, and End-Results (SEER) cancer registries. We performed life-table analysis, the log-rank test, and Cox proportional hazards regression to compare the time to fatal MI from diagnosis between left-sided and right-sided cases, censoring deaths from other causes.


RESULTS
Among irradiated patients, the relative risk (RR) for fatal MI in women with left-sided breast cancer was 1.17 (95% confidence interval [CI], 1.01 to 1.36), controlling 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 irradiated 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 with left-sided compared with right-sided breast cancer, but not among patients aged 60 years or older. Among irradiated local-stage cases, the risk for those with left-sided breast cancer was not significantly elevated in either age category. Analysis of 5-year conditional 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).


CONCLUSIONS
Adjuvant RT for left-sided breast cancer diagnosed in women younger than 60 years of age is associated with a higher risk for fatal MI 10 to 15 years later compared with adjuvant RT for right-sided cases.
Paszat
L F
LF
Department of Oncology, Kingston Regional Cancer Centre, Ontario, Canada. lpaszat@cancercare.on.ca
Mackillop
W J
WJ
Groome
P A
PA
Boyd
C
C
Schulze
K
K
Holowaty
E
E
D000328:Adult; D001943:Breast Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D015993:Life Tables; D008875:Middle Aged; D009203:Myocardial Infarction / Q000209:etiology / Q000401:mortality*; D016016:Proportional Hazards Models; D018714:Radiotherapy, Adjuvant / Q000009:adverse effects; D012189:Retrospective Studies; D012307:Risk Factors; D018426:SEER Program