Dr. Vicini on the Potential Utility of the DCISionRT Test in HER2+ DCIS of the Breast

Frank A. Vicini, MD, radiation oncologist, GenesisCare, discusses the potential utility of using the DCISionRT test to determine treatment benefit in the phase 3 NRG-NSABP-B43 trial (NCT00769379) in HER2-positive ductal carcinoma in situ (DCIS) of the breast.

Previous research on HER2-positive versus HER2-negative DCIS has elucidated an association between HER2 status and increased risk of local recurrence. The prospective, randomized NRG-NSABP-B43 trial evaluated whether the efficacy of whole breast radiation therapy increased with 2 doses of trastuzumab (Herceptin) in patients with HER2-positive DCIS who had previously undergone breast conservation surgery, Vicini begins. Although primary data from this trial did not show a statistically significant reduction in ipsilateral breast recurrence (IBR) with the regimen, a modest improvement in local control was observed.

In a poster presented at the 2022 San Antonio Breast Cancer Symposium, researchers assessed the rate of IBR in a large, multicenter population of HER2-positive patients to determine clinical benefit from radiation therapy after breast conserving surgery, Vicini explains. The DCISionRT biomarker test was used to evaluate a patient’s residual risk subtype and predict an individual’s invasive 10-year recurrence risk after breast conserving surgery with or without radiation therapy.

Patients identified as low risk were expected to achieve similar rates of recurrence with radiation therapy while those in the high-risk group were expected to have significantly lower recurrence rates with radiation therapy, Vicini continues. Clinicopathologic features associated with recurrence risk were also accounted for and were used as a comparison to the DCISionRT biosignatures. The results showed that DCISionRT was a better predictor of 10-year prognosis and radiation therapy benefit vs clinicopathologic criteria alone.

This classification of patients based on residual risk suggests that further analysis with the predictive 7-gene biosignature DCISionRT test could help clarify the impact of trastuzumab on patient outcomes and predict which patient subtypes will benefit most from the investigational regimen explored in NRG-NSABP-B43, he concludes.