As reported in the Journal of Clinical Oncology by Thorsen et al, 15-year follow-up of the Danish Breast Cancer Group Internal Mammary Node study indicates continued survival benefit with internal mammary node irradiation in women with right breast tumors vs without such therapy in those with left breast tumors in early node-positive breast cancer.
An earlier report from the study showed improved overall survival at 8 years in women receiving internal mammary node irradiation.
Study Details
In the nationwide prospective cohort study, 3,089 women received adjuvant radiotherapy; a total of 1,491 with right-sided disease received internal mammary node irradiation and 1,590 with left-sided disease did not. Other treatments were independent of laterality.
The primary endpoint was overall survival. Secondary endpoints were distant recurrence and breast cancer mortality. All analyses were conducted in the intention-to-treat population.
Key Findings
Median follow-up was 14.8 years at the time of analysis. Overall, 96% of patients with right-sided breast cancer received internal mammary node irradiation and 90% of patients with left-sided disease did not.
“In patients with node-positive early breast cancer treated with [internal mammary node irradiation] or without [internal mammary node irradiation] depending on breast cancer laterality, [the radiotherapy strategy] reduced the risk of distant recurrence and death from breast cancer, thereby improving long-term survival.”— Thorsen et al
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Death occurred in 589 patients with and 701 patients without internal mammary node irradiation, with 15-year overall survival rates of 60.1% vs 55.4% (hazard ratio [HR] adjusted for prognostic factors = 0.86, 95% confidence interval [CI] = 0.77–0.96, P = .007).
Distant recurrence was observed in 523 vs 602 patients, with 15-year risks of distant recurrence of 35.6% vs 38.6% (adjusted HR = 0.88, 95% CI = 0.79–0.99, P = .04).
Death due to breast cancer occurred in 467 vs 537 patients, with 15-year morality rates of 31.7% vs 33.9% (adjusted HR = 0.88, 95% CI = 0.78–1.00, P = .05). The frequency of deaths due to other causes was similar between groups.
The investigators concluded: “In patients with node-positive early breast cancer treated with [internal mammary node irradiation] or without [internal mammary node irradiation] depending on breast cancer laterality, [the radiotherapy strategy] reduced the risk of distant recurrence and death from breast cancer, thereby improving long-term survival.”
Lise B.J. Thorsen, MD, PhD, of the Department of Experimental Clinical Oncology, Aarhus University Hospital, is the corresponding author for the Journal of Clinical Oncology article.
Disclosure: The study was supported by the Danish Cancer Society and Danish Comprehensive Cancer Center Radiotherapy. For full disclosures of the study authors, visit ascopubs.org.
