Conference Coverage

Genomic signature predicts safety of omitting RT in early breast cancer



A novel 16-gene panel based on the biology of locoregional recurrence in early invasive breast cancer can both identify patients with a low risk of recurrence if they were to skip postsurgery radiation therapy, and predict which patients would be unlikely to benefit from adjuvant radiation, investigators reported.

Among 354 patients with stage I or II invasive estrogen receptor–positive (ER+), HER2-negative breast cancers who did not receive adjuvant systemic therapy, the genomic signature, dubbed POLAR (Profile for the Omission of Local Adjuvant Radiation) was prognostic for locoregional recurrence in patients who did not undergo radiation therapy, reported Martin Sjöström, MD, PhD, of the University of California, San Francisco, and colleagues.

They reported their findings in a poster presented during the American Society of Clinical Oncology (ASCO) annual meeting (Abstract 512).

“This is to our knowledge the first radiation-omission signature that is both prognostic and predictive: prognostic for outcomes in the absence of radiation, and predictive of benefits,” coauthor Corey Speers MD, PhD, of the University of Michigan, Ann Arbor, said in an interview.

The investigators conducted a retrospective analysis of data on patients enrolled in the SweBCG 91 RT trial, in which 1,187 patients with T1-2N0M0 breast cancer underwent a standardized radical sector resection and were then randomly assigned to either postoperative radiotherapy or no further treatment.

As the investigators reported in a long-term follow-up study presented in 2010 at the San Antonio Breast Cancer Symposium, the addition of postoperative radiation did not significantly affect overall survival, but was associated with a significant improvement in recurrence-free survival.

In the study presented at ASCO 2021, Dr. Sjöström and colleagues in Sweden, the United States, and Canada sought to determine whether they could identify a genomic signature that would identify women at very low risk for recurrence who could safely be spared from radiotherapy.

They focused on those patients in the study with ER+, HER2-negative tumors who did not receive adjuvant systemic therapy. The patients were divided into a training cohort of 243, and a validation cohort of 354 patients.

The investigators performed transcriptome-wide profiling of tumors, and identified both biological gene sets and individuals genes associated with locoregional recurrence among patients in the training set who did not receive radiotherapy.

The final POLAR genomic signature, containing 16 genes, was locked prior to testing in the validation cohort.

In a multivariable Cox model adjusting for age, grade, tumor size and luminal A vs. luminal B subtype, the POLAR gene set was prognostic for locoregional recurrence, with a hazard ratio (HR) of 1.7 (P < .001).

The 10-year locoregional recurrence rate for patients in the POLAR low-risk category who had not received radiation was 7%, and there was no significant benefit for POLAR low-risk patients who did receive radiation (HR 1.1, P = ns).

In contrast, patients classified as POLAR high risk who received radiotherapy had significantly lower risk for locoregional recurrence than high-risk patients who did not receive radiotherapy (HR 0.43, P = .0053).

Dr. Speers said that the POLAR signature appears to be unique in its ability to discriminate radiation-omission risk.

“At least looking in this cohort in the Swedish trial, none of other previously derived signatures – Mammaprint, ProSigna, Oncotype – were prognostic or predictive of locoregional recurrence events with radiation,” he said.

The investigators are currently exploring the POLAR signature in other clinical trials in which patients were randomized to receive radiation or no radiation.


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