By Kate O’Rourke
Omitting radiation after breast-conserving surgery may not impact 10-year survival rates in women 65 years or older with hormone receptor-positive, early invasive breast cancer, suggest long-term follow up results from the PRIME II trial. The findings were presented at the 2020 San Antonio Breast Cancer Symposium.
Study investigators recommend the “omission of postoperative radiotherapy as a reasonable option” for patients with pT1-2 (up to 3 cm) grade 1-2 tumors, as there is no evidence that it increases the risk of metastatic disease or impacts survival, said Ian Kunkler, FRCPE, professor of clinical oncology at the Western General Hospital, University of Edinburgh, who presented the findings.
Dr. Kunkler said he would be cautious in omitting radiotherapy for patients with low ER tumors.
Researchers launched the randomized PRIME II trial because of sparse Level 1 evidence on the impact on local control and quality of life of postoperative radiotherapy after breast conserving surgery and adjuvant endocrine therapy in low-risk, older breast cancer patients. PRIME II aimed to evaluate the impact of omitting whole breast irradiation on local control at 10 years after breast conserving therapy and adjuvant endocrine therapy in low-risk older breast cancer patients (Abstract GS2-03).
Researchers recruited 1,326 patients over 6 years between 2003 and 2009 and randomized them to whole breast irradiation (40-50 Gray in 15-25 fractions) or to no whole breast irradiation. The two arms were well-balanced for age, tumor size, grade, the presence of lymphovascular invasion, adjuvant endocrine therapy, and preoperative endocrine therapy.
The majority of patients had tumors less than 20 millimeters and 95% of patients had grade 1 or 2 tumors; a minority of patients had grade 3 tumors. In terms of eligibility, tumors were pathologically less or equal to 3 cm, and patients had to have axillary node negative cancer, have excision margins of at least a millimeter, and have tumors that were ER or PGR-positive with levels greater than zero. Both preoperative endocrine therapy and postoperative adjuvant endocrine therapy were allowed. Patients who had a combination of grade 3 histology were excluded. The median follow up was 7.3 years.
The researchers found that radiotherapy reduced the 10-year actuarial rates of ipsilateral breast tumor recurrence from 9.8% to 0.09% (P=0.0008). In terms of secondary endpoints, there was a small increase in regional recurrence in the no radiotherapy group (2.3% vs. 0.5%; P=0.014), but no difference in distant recurrence, contralateral breast cancer or new non-breast cancers.
The researchers found no difference between the two study cohorts in terms of overall survival or metastasis-free survival.
Of note, 6.6% of patients died from breast cancer, including eight patients in the no radiotherapy group and three patients in the irradiated group. In an unplanned subgroup analysis by estrogen receptor (ER) status, patients who had low level ER had a much higher local recurrence rate at 10 years, compared to those with high level ER (18.8% vs 9.2%; P=0.007).