Abstract P2-08-01: Validation of a 16-gene genomic signature to identify early-stage invasive breast cancer patients who may omit radiotherapy

Abstract

Abstract Background While whole breast radiotherapy has been standard of care for invasive breast cancer patients treated with breast conserving surgery, not all women may benefit from radiotherapy. Recently, we demonstrated that a 16-gene signature named Profile for the Omission of Local Adjuvant Radiotherapy (POLAR) could identify breast cancer patients with HR+, HER2- tumors treated with breast conserving surgery alone with a 10-year locoregional recurrence risk of less than 10%. Methods In this study, we apply the signature to patients enrolled in the Princess Margaret Trial, a randomized trial where patients age 50 years or older were randomized to radiotherapy and tamoxifen or tamoxifen alone after breast conserving surgery. Tissue from 132 patients with HR+, HER2- tumors were available for gene expression analysis. Results For women treated with tamoxifen alone after breast conserving surgery, POLAR identified low risk women with a 7% risk of locoregional recurrence at 10 years. Comparison to POLAR-low patients treated with adjuvant radiotherapy did not demonstrate a significant benefit from radiotherapy (HR=1.5[0.14-16], p=0.74). POLAR-high patients not treated with radiotherapy had a 22% risk of locoregional recurrence at 10 years. Comparison to POLAR-high patients treated with adjuvant radiotherapy demonstrated a significant benefit from standard radiotherapy (HR=0.25[0.07-0.92], p=0.038). Conclusions These data suggest that the POLAR genomic signature may be used to identify patients with a low risk of locoregional recurrence without significant benefit from adjuvant radiotherapy. Patients with low POLAR scores may potentially be candidates for radiation therapy omission when treated with breast conserving surgery and tamoxifen. Citation Format: Anthony Fyles, S. Laura Chang, Katrina Rey-McIntyre, Wei Shi, Felix Feng, Corey Speers, Lori Pierce, David McCready, Fei-Fei Liu. Validation of a 16-gene genomic signature to identify early-stage invasive breast cancer patients who may omit radiotherapy [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-08-01.