Novel Gene Panel Predicts Who Can Skip RT in Early Breast Cancer

Neil Osterweil

June 08, 2021

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, 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).

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.

"A True Victory"

Invited discussant Benjamin D. Smith, MD, of the University of Texas MD Anderson Cancer Center in Houston, pointed out that in randomized clinical trials, approximately 60% of patients treated for early breast cancer did not experience recurrence in the absence of radiation, and that radiation prevented recurrence in about 30%, while about 10% experienced recurrence despite receiving radiation.

He said that the study by Sjöström and colleagues asks the question "can we use molecular factors to help identify patients who will not recur with lumpectomy alone without radiation therapy?"

The 60% of patients who will not experience recurrence in the absence of radiation can be categorized into two subpopulations: those with no residual malignant clonogens – the population included in this study by Sjöström and colleagues – and those with residual clonogens in the breast or elsewhere in the body that are sensitive to adjuvant endocrine therapy.

He said that the 7% 10-year risk of recurrence among patients in the POLAR low-risk group, who had neither radiation nor endocrine therapy, "is an exceptional outcome, which should be applauded, and I would point out that this risk of local recurrence of only 7% is at least in the same ballpark as the risk of recurrence that we accept every day when we treat early stage breast cancer patients with mastectomy alone, so this is a true victory.

"When we reflect on these provocative results from Sjöström and colleagues, it prompts in mind the question, could there be a group of patients with early breast cancer for whom a true 'one-and-done' strategy could be effective and safe?" Smith said.

Getting there will require a multidisciplinary, multimodality approach, involving imaging features of the primary tumor, clinical and pathologic features, and molecular information such as that provided by the POLAR genomic signature, he said.

The study was supported by PFS Genomics. Sjöström reported institutional funding from PFS Genomics. Speers disclosed stock and other ownership interests in the company, and he has applied for a patent on methods and genomic classifiers for prognosis of breast cancer and predicting benefit from adjuvant radiotherapy. Smith reported an equity interest in Oncora Medical, and an uncompensated relationship with the American Society for Radiation Oncology.

This article originally appeared on, part of the Medscape Professional Network.


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