Abstract P2-10-07: A prospective clinical utility study of the impact of the 21-gene recurrence score (RS) assay in the treatment of estrogen receptor positive (ER+), HER2 negative (HER2-), 1-3 node positive (N+) breast cancer (BC)

Abstract

Abstract Background: The 21-gene RS is routinely used in node negative ER+, HER2- BC to help guide chemotherapy treatment decision making. There is emerging use of the RS in limited N+ BC, though the results from the randomized clinical trial (RxPONDER) is pending. The objective of the study is to determine whether the results of the 21-gene RS will alter physician treatment decisions in ER+ HER2- limited N+ BC. Methods: Consenting patients (pts) with ER+, HER2-, 1-3 N+ (microscopic or macroscopic) early stage BC participated in this prospective, multi-center British Columbia Cancer Agency (BCCA) study. Treating physicians completed a questionnaire after an initial visit with the patient to document their treatment recommendation before obtaining the RS assay. At a subsequent visit, the assay result and final treatment recommendations were discussed and physicians completed a second questionnaire on the final treatment plan. The statistical assumption of the study was based upon anticipating an overall treatment decision change rate (from chemo-hormonal therapy to hormone only, or vice-versa) to be at least 30%. Results: Out of 84 pts enrolled, 82 went on to have RS testing. 57% of pts had T1 tumors, 40% T2 and 2% T3 tumors. The majority of pts (77%) had N1 macroscopic disease compared to 23% that had microscopic nodal involvement. 63% of cases were grade 2, followed by 23% grade 1 and 14% grade 3. 60% of RS were low (<18), 33% intermediate (18-30) and 7% were high (>30). In 53% of cases there was an altered treatment plan (49% switched from chemo-hormonal therapy to hormone only, and 4% switched from hormone only to chemo-hormonal therapy). Of the 49% that switched to hormone only, 68% had a low RS and 33% had an intermediate RS. All 4% that switched to chemo-hormonal therapy had an intermittent RS. Conclusions: This multi-centered Canadian study showed that in 53% of cases, treatment recommendations were changed based on the RS. This suggests that there is clinical utility for the RS in 1-3 N+, ER+, and HER2- breast cancer. Citation Format: Sun J, Fenton D, Baxter S, Chan A, Roberts S, Feng X, Lohrisch C, Gelmon K, Shenkier T, Chia S. A prospective clinical utility study of the impact of the 21-gene recurrence score (RS) assay in the treatment of estrogen receptor positive (ER+), HER2 negative (HER2-), 1-3 node positive (N+) breast cancer (BC) [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-10-07.