SAN ANTONIO – Avoiding whole-breast radiation therapy is a reasonable – and even attractive – option for many older women with early-stage breast cancer, according to the results of the Postoperative Radiotherapy in Minimum-Risk Elderly (PRIME II) trial.
The patient population identified in PRIME II as being suitable for omission of postoperative radiotherapy on the basis of a relatively benign natural history consists of women aged 65 or older who are on adjuvant hormone therapy after undergoing lumpectomy with clear margins for estrogen receptor–rich, axillary node–negative breast cancer.
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PRIME II was a six-country trial in which 1,326 patients 65 or older with hormone receptor–positive early breast cancer were randomized to radiotherapy or no radiotherapy following breast-conserving surgery and endocrine therapy. The 5-year actuarial rate of ipsilateral breast cancer recurrence – the primary study endpoint – was 1.3% in those who received radiotherapy and 4.1% in those who did not, Dr. Ian H. Kunkler reported at the San Antonio Breast Cancer Symposium.
The 5-year actuarial rate of overall survival was 94.2% in patients randomized to radiotherapy and closely similar at 93.8% in the no-radiotherapy group, added Dr. Kunkler, professor of clinical oncology at the University of Edinburgh.
The relative benefit of radiotherapy was even smaller in the 91% of subjects who had estrogen-rich tumors as defined by an ER score of at least 7. They had a local recurrence rate of 3.2% with radiotherapy and 0.8% without. While that absolute 2.4% difference was statistically significant, it is arguably not clinically meaningful. For every 100 women who fit the description carefully defined in PRIME II and who undergo radiotherapy, three will have a recurrence prevented, one will have a recurrence anyway, and 96 will have had treatment that was not beneficial, he said.
Dr. Ian H. Kunkler
"I think we’re really at the cusp of overtreatment here. I think it’s a matter for discussion between the physician and patient as to whether that very modest benefit is worth the potential complications of radiotherapy and the burdens of ongoing treatment, as well as the costs to the health service. Older patients find radiotherapy very burdensome, the relative benefits are very small, and there is no compromise in terms of overall survival with its omission," Dr. Kunkler said.
An important caveat: Among the 9% of patients with low estrogen receptor status, the local recurrence rate was 11.1% with no radiotherapy compared to zero with radiation.
"This is a group for whom radiotherapy should not be omitted," Dr. Kunkler declared.
More than one-half of all early breast cancers present in women aged 65 or older. While postoperative radiotherapy after lumpectomy has been the standard of care regardless of age and other risk factors, there has been only sparse high-quality supporting evidence for this practice in older patients.
Dr. Kunkler estimated that the PRIME II findings are generalizable to 60%-70% of all breast cancer patients over age 65. He predicted that the PRIME II study will "very likely" alter practice in the United Kingdom, and symposium codirector Dr. C. Kent Osborne predicted that the study will be practice changing in the United States as well.
Dr. C. Kent Osborne
"When I was in training, everybody thought that more was better: more drug treatment, more radiation, more surgery, high-dose chemotherapy, and bone marrow transplant. As we’ve evolved over the last 3 decades, that’s turning out not to be the case. I think we’re gradually doing less and less treatment, either with radiotherapy or with surgery, to control the local disease in appropriate patients. And I think more and more people will begin to accept it," said Dr. Osborne, director of the Dan L. Duncan Cancer Center and the Lester and Sue Smith Breast Center at Baylor College of Medicine, Houston.
PRIME II was funded by the Chief Scientist Office for Scotland. Dr. Kunkler declared having no conflicts of interest.