Risk of heart disease in relation to radiotherapy and chemotherapy with anthracyclines among 19,464 breast cancer patients in Denmark, 1977–2005

BACKGROUND AND PURPOSE The risk of heart disease subsequent to breast cancer radiotherapy was examined with particular focus on women receiving anthracycline-containing chemotherapy. MATERIAL AND METHODS Women diagnosed with early-stage breast cancer in Denmark, 1977-2005, were identified from the register of the Danish Breast Cancer Cooperative Group, as was information on cancer-directed treatment. Information on heart disease was sought from the Danish National Patient and Cause of Death Registries. Incidence rate ratios were estimated comparing left-sided with right-sided cancer (IRR, LvR), stratified by calendar year, age, and time since breast cancer radiotherapy. RESULTS Among 19,464 women receiving radiotherapy, the IRR, LvR, was 1.11 (95% CI 1.03-1.20, p=0.005) for all heart disease and among those also receiving anthracyclines the IRR, LvR, was 1.32 (95% CI 1.02-1.70, p=0.03). This risk was highest if the treatment was given before the age of 50years (IRR, LvR, 1.44, (95% CI 1.04-2.01) but there was no significant trend with age or time since treatment. CONCLUSIONS Radiotherapy for left-sided breast cancer is associated with a higher risk of heart disease than for right-sided with the largest increases seen in women who also received anthracycline-containing chemotherapy.