Side Effects 15 Years After Lymph Node Irradiation in Breast Cancer: Randomized EORTC Trial 22922/10925.

Background: Uncertainty about the benefit-risk ratio of regional lymph node irradiation led to varying clinical protocols. We investigated long-term late side effects after internal mammary and medial supraclavicular (IM-MS) lymph node irradiation to improve shared decision making.
Methods: The multicenter European Organization for Research and Treatment of Cancer trial (ClinicalTrials.gov, NCT00002851) randomly assigned stage I-III breast cancer patients with involved axillary nodes and/or a medially located primary tumor. We analyzed late side effects both longitudinally at every follow-up and cross-sectionally at 5-year intervals. All statistical tests were 2-sided.
Results: Between 1996 and 2004, 46 departments from 13 countries accrued 4004 patients. Median follow-up was 15.7 years. Longitudinal follow-up data showed cumulative incidence rates at 15 years of 2.9% (95% confidence interval [CI] = 2.2% to 3.8%) vs 5.7% (95% CI = 4.7% to 6.9%) (P < .001) for lung fibrosis, 1.1% (95% CI = 0.7% to 1.7%) vs 1.9% (95% CI = 1.3% to 2.6%) (P = .07) for cardiac fibrosis, and 9.4% (95% CI = 8.0% to 10.8%) vs 11.1% (95% CI = 9.6% to 12.7%) (P = .04) for any cardiac disease when treated without or with IM-MS lymph node irradiation. There was no evidence for differences between left- and right-sided breast cancer (Wald χ2 test of treatment by breast side interaction, P = .33 and P = .35, for cardiac fibrosis and for any cardiac disease, respectively). The cumulative incidence probabilities of cross-sectionally reported side effects with a score of 2 or greater at 15 years were 0.1% (95% CI = 0.0% to 0.5%) vs 0.8% (95% CI = 0.4% to 1.4%) for pulmonary (P = .02), 1.8% (95% CI = 1.1% to 2.8%) vs 2.6% (95% CI = 1.8% to 3.7%) for cardiac (P = .15), and 0.0% (95% CI not evaluated) vs 0.1% (95% CI = 0.0% to 0.4%) for esophageal (P = .16), respectively. No difference was observed in the incidence of second malignancies, contralateral breast cancer, or cardiovascular deaths.
Conclusions: The incidence of late pulmonary side effects was statistically significantly higher after IM-MS lymph node irradiation, as were some of the cardiac events, without a difference between left- and right-sided treatments. Absolute rates and differences were very low, without increased non-breast cancer-related mortality, even before introducing heart-sparing techniques.
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