Omission of radiotherapy is a reasonable option for women 65 years or older who receive hormone therapy after breast-conserving surgery for hormone receptor-positive, axillary node-negative breast cancer. These results from the PRIME 2 trial were presented at the 2013 San Antonio Breast Cancer Symposium, December 10-14, 2013.

“Radiotherapy has been known to reduce the risk of breast cancer recurrence three- to four-fold. However, what our trial has shown is that, although this is still the case, the proportion of women who will actually have a recurrence without radiotherapy is very small (less than 5%), 5 years after treatment,” said Ian Kunkler, FRCR, professor of clinical oncology at the Edinburgh Cancer Research Center in the University of Edinburgh in Scotland, United Kingdom. “We have identified a subgroup of older patients at sufficiently low risk of recurrence for whom omission of postoperative radiotherapy after breast-conserving surgery and adjuvant endocrine therapy is a reasonable option.”

“What this study shows is that, for every 100 women (from our selected population) treated with radiotherapy, one will have a recurrence anyway, four will have a recurrence prevented, but 95 will have had unnecessary treatment,” said Kunkler. “Once a patient has had radiotherapy, they are unable to have it again on the same breast. Had these women not had radiotherapy, they would have been able to have minor surgery and radiotherapy following a recurrence. Besides, radiotherapy carries its own health risks, particularly in the elderly, as well as the inconvenience of travel for daily treatment for 3 or 4 weeks.

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“Allowing us to defer radiotherapy in this group of patients until a recurrence occurs will be of benefit to the patient and to the health service,” said Dr. Kunkler.

PRIME 2 is an international, phase III randomized, controlled trial that set out to address the question of whether whole-breast radiotherapy can be omitted in carefully defined groups of older patients receiving appropriate therapy. The primary endpoint of this trial is recurrence of breast cancer in the same breast, known as ipsilateral breast tumor recurrence (IBTR).

The investigators found that, at 5 years, 1.3% of patients who received radiotherapy had IBTR, and 4.1% of patients who did not receive radiotherapy had IBTR.

Between 2003 and 2009, 1,326 patients were enrolled in the trial; 658 patients were randomly assigned to receive radiotherapy and 668 did not receive radiotherapy. All participants were 65 years or older; had hormone-positive, low-grade breast cancer; did not have the disease in lymph nodes adjacent to the breast (axillary node-negative); did not have metastasis; had cancer-free breast tissue margins where the tumor was surgically removed; and received hormone therapy.

The investigators found that at 5 years, between patients who received radiotherapy and those who did not, there was no significant difference in overall survival (97% vs 96.4%), regional recurrence (0.5% vs 0.8%), or breast cancer in the opposite breast (0.5% vs 0.7%).