Omission of Radiation Therapy in Older Patients with Breast Cancer

De-escalation of therapy, where appropriate, can potentially have no detrimental effect on outcome while decreasing morbidity and cost. The role of adjuvant breast radiation therapy (RT) in older patients with lower-risk, hormone-sensitive breast cancer has been one such scenario where less is more. Investigators now report mature results from the PRIME II trial, a multicenter, randomized, phase 3 clinical trial of whole-breast RT during 3 to 5 weeks versus no RT. Eligible patients were aged 65 or older with node-negative, estrogen receptor (ER)–positive tumors ≤3 cm who underwent breast-conserving therapy and received adjuvant endocrine therapy. HER2 status was not evaluated at the initiation of the trial.

A total of 1326 patients (median age, 70) were randomized between 2003 and 2009. Only 10% had ER-low disease. Tamoxifen was the most commonly prescribed endocrine therapy. Median follow-up was 9.1 years.

The cumulative incidence of local recurrence — the primary outcome — within 10 years was 9.5% in patients not receiving RT, compared with 0.9% in those receiving RT (hazard ratio, 10.4; P<0.001). Breast cancer–specific survival at 10 years was similar in the two groups (≈97%) as was overall survival (≈81%). Among patients who did not receive RT, risk for local recurrence was higher in those who were not optimally adherent to adjuvant endocrine therapy than in those who were adherent.