Omission of whole-breast radiation therapy was associated with higher incidence of recurrence but no difference in survival in patients with lower-risk, ER-positive 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 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 multicentre, randomised, phase 3 clinical trial of whole-breast radiation therapy during three to five weeks versus no radiation therapy. Eligible patients were aged 65 years or older with node-negative, estrogen receptor (ER)-positive tumours 3 cm or less in size 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 years) were randomised 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 radiation therapy, compared with 0.9% in those receiving radiation therapy (hazard ratio, 10.4; p<0.001). Breast cancer-specific survival at 10 years was similar in the two groups (about 97%) as was overall survival (about 81%). Among patients who did not receive radiation therapy, risk for local recurrence was higher in those who were not optimally adherent to adjuvant endocrine therapy than in those who were adherent.

Comment: These findings support omission of breast radiation therapy in older patients with ER-positive tumours and other favourable characteristics who will receive five years of adjuvant endocrine therapy. Although the rate of local recurrence is higher without radiation therapy, many patients can undergo repeat lumpectomy and possible radiation therapy should a recurrence occur. Most importantly, omission of radiation therapy has no effect on survival, particularly if patients remain adherent to adjuvant endocrine therapy. The importance of adherence must be emphasised in follow up.

William J. Gradishar, MD
Professor of Medicine and Director of Breast Medical Oncology, Robert H. Lurie Comprehensive Cancer Center, Northwestern University Feinberg School of Medicine, Chicago, USA.

Kunkler IH, et al. Breast-conserving surgery with or without irradiation in early breast cancer. N Engl J Med 2023; 388: 585-594.

This summary is taken from the following Journal Watch titles: Oncology and Hematology, General Medicine, Ambulatory Medicine