TOPLINE:
The Profile for the Omission of Local Adjuvant Radiation (POLAR) biomarker, a 16-gene molecular signature, can help predict locoregional recurrence in patients with ER-positive early breast cancer following breast-conserving surgery as well as which patients will benefit most from adjuvant radiotherapy. Overall, patients with a high POLAR score derived a significant benefit from adjuvant radiotherapy, while those with a low score did not and might consider forgoing radiotherapy.
METHODOLOGY: Radiation therapy after breast-conserving surgery has been shown to reduce the risk for locoregional recurrence and is a standard approach to manage early breast cancer. However, certain patients with low locoregional recurrence risks may not necessarily benefit from adjuvant radiation, but there has not been a commercially available molecular test to help identify which patients that might be. In the current analysis, researchers assessed whether the POLAR biomarker test could reliably predict locoregional recurrence as well as identify patients who would not benefit from radiotherapy. The meta-analysis used data from three randomized trials — Scottish Conservation Trial, SweBCG91-RT, and Princess Margaret RT trial — to validate the POLAR biomarker test in patients with low-risk, HR-positive, HER2-negative, node-negative breast cancer. The analysis included 623 patients (ages 50-76), of whom 429 (69%) had high POLAR scores and 194 (31%) had low POLAR scores. The primary endpoint was the time to locoregional recurrence, and secondary endpoints included evaluating POLAR as a prognostic factor for locoregional recurrence in patients without radiotherapy and effect of radiotherapy in patients with low and high POLAR scores. TAKEAWAY: Patients with high POLAR scores demonstrated a significant benefit from radiotherapy. The 10-year locoregional recurrence rate was 7% with radiotherapy vs 20% without radiotherapy (hazard ratio [HR], 0.37; P <.001). Patients with low POLAR scores, however, did not experience a significant benefit from radiotherapy. In this group, the 10-year locoregional recurrence rates were similar with and without radiotherapy (7% vs 5%, respectively; HR, 0.92; P=.832), indicating that radiotherapy could potentially be omitted for these patients. Among patients who did not receive radiotherapy (n=309), higher POLAR scores predicted a greater risk for recurrence, suggesting the genomic signature has prognostic value. There is no evidence, however, that POLAR predicts radiotherapy benefit or predicts patients’ risk for distant metastases or mortality. IN PRACTICE:
“This meta-analysis from three randomized controlled trials clearly demonstrates the clinical potential for POLAR to be used in smaller estrogen receptor positive node negative breast cancer patients to identify those women who do not appear to benefit from the use of post-operative adjuvant radiotherapy,” the authors wrote. ” This classifier is an important step towards molecularly-stratified targeting of the use of radiotherapy.”
SOURCE:
The study, led by Per Karlsson, MD, PhD, University of Gothenburg, Sweden, was published online in the Journal of the National Cancer Institute.
LIMITATIONS:
One cohort (SweBCG) had limited use of adjuvant systemic therapy, which could affect generalizability. Additionally, low numbers of patients with low POLAR scores in two trials could affect the observed benefit of radiotherapy.
DISCLOSURES:
This study was supported by the Breast Cancer Institute Fund (Edinburgh and Lothians Health Foundation), Canadian Institutes of Health Research, Exact Sciences Corporation, PFS Genomics, Swedish Cancer Society, and Swedish Research Council. One author reported being an employee and owning stock or stock options or patents with Exact Sciences. Several authors reported having various ties with various sources including Exact Sciences.
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