Abstract P4-02-12: Validation of Profile for the Omission of Local Adjuvant Radiotherapy (POLAR) in early-stage invasive breast cancer patients of the Scottish Conservation Trial

Abstract

Abstract Background: Adjuvant whole breast radiotherapy (RT) is provided to almost all women with early-stage invasive breast cancer after breast conserving surgery and appropriate systemic therapy. While there is increasing interest to personalize the use of RT based on molecular profiling, to date, there is no molecular signature available to reliably assess the benefit of radiotherapy after surgical resection. Here we assess the ability of a 16-gene signature named Profile for the Omission of Local Adjuvant Radiotherapy (POLAR) to identify who may be suitable candidates for radiotherapy omission in patients of the Scottish Conservation Trial. Methods: The POLAR signature was applied to archival tissue from the Scottish Conservation Trial, which randomized 585 patients with stage I-II breast cancer, tumor size < 4 cm, and age ≤70 years old to receive RT or not. The archival tissue was measured for ER (ER+ >10%), PgR (PgR+ ≥20%), Ki67 (Ki67 high ≥14%), and HER2 (HER2+ defined as HER2 over-expressed or amplified). 26% received adjuvant chemotherapy, the remainder received tamoxifen 20 mg/daily for 5 years. Cox models for the locoregional recurrence (LRR) endpoint tested the association between treatment arms separately for patients with a low and high POLAR score using a pre-specified cut point. Cumulative incidences were computed, with distant metastasis and death without recurrence considered competing events. Results: 224 patients had tissue available and complete clinical data for analysis, 40 (18%) were node-positive. The distribution of clinicopathologic variables between the RT and no RT arms remained balanced. 43% were ER+/PgR+/Ki67 low/HER2-, 31% were ER+/HER2-/Ki67 high or PgR-, 5% were HER2+, and 13% were triple negative. The continuous standardized POLAR score was prognostic for LRR in the no RT arm after adjusting for relevant covariates (HR=1.78 [1.20-2.64], p=0.003). For patients with a POLAR-high score, the 10-year LRR rate was 31% [21%-42%] for patients not receiving RT and 8% [3%-15%] for patients receiving RT (HR 0.36 [0.19-0.69], p=0.0022). For patients with a POLAR low score, the 10-year LRR rates were 20% [10%-33%] for patients not receiving RT and 6% [1%-18%] for patients receiving RT; HR=0.28 [0.08-0.98], p=0.046). In the subgroup of node-negative patients with ER+/HER2-negative tumors (N=137), there was a statistically significant RT benefit for patients with a POLAR high score (HR=0.31 [0.11-0.88], p=0.028) but not for patients with a POLAR low score (HR=0.5 [0.1-2.4], p=0.39). Conclusions: For patients with early-stage invasive breast cancer treated with breast-conserving surgery without RT, POLAR is prognostic for LRR and may refine the selection of “low risk” for omission of RT. Citation Format: Karen J. Taylor, John MS Bartlett, John Bennett, S. Laura Chang, Bradley Arrick, Frederick Baehner, Joseph F. Loane, Tammy Piper, Elizabeth Mallon, Joanna Dunlop, Wilma J. Jack, Jacqueline Caldwell, Ian Kunkler, Linda J. Williams, Corey W. Speers, Felix Y. Feng, Lori Pierce, David A. Cameron. Validation of Profile for the Omission of Local Adjuvant Radiotherapy (POLAR) in early-stage invasive breast cancer patients of the Scottish Conservation Trial [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-02-12.