Abstract P1-10-12: Evaluating the Impact of Prosigna® Testing on Adjuvant Chemotherapy Decisions in Early-Stage ER-Positive, HER2-Negative Breast Cancer: A UK Study

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Abstract Multi-gene assays are recommended for guiding adjuvant chemotherapy decisions in early-stage ER-positive, HER2-negative breast cancer. This study aimed to evaluate the impact of Prosigna® testing on clinical decisions and to identify factors that predict the Prosigna® risk stratification outcomes. Women with ER-positive, HER2-negative breast cancer, eligible for chemotherapy based on intermediate risk of distant recurrence (using tools such as Predict or the Nottingham Prognostic Index), were retrospectively identified from three UK hospitals. Patient and tumor characteristics, Prosigna® test results, and final treatment decisions were collected. Outcome parameters included disease progression and overall survival. Multinomial logistic regression identified key predictors of low, intermediate, and high-risk categories of Prosigna® test results. Among 363 patients with a median age of 61, 71% were post-menopausal, and 48% had grade 3 tumors. Based on Prosigna® results, 60% (n=216) avoided chemotherapy despite clinical indications, while 14% (n=52) without initial indications were escalated to receive chemotherapy. Anthracycline and Taxane-based regimens were most common (76%), followed by Docetaxel and Cyclophosphamide (24%). At a median follow-up of 2 years, 2.4% (n=9) had disease progression, all of whom received chemotherapy. High-risk and intermediate-risk (Luminal B subtype) patients were primarily offered chemotherapy. Tumor grade emerged as the most significant predictor across all Prosigna® risk categories, with a positive coefficient for high risk and negative coefficients for intermediate and low risk. NPI and Predict score also influenced risk stratification, positively impacting high and intermediate risk categories and negatively impacting low risk. Age, tumor size, and LVSI had smaller, less consistent influences. The model achieved an overall accuracy of 41%, with the highest precision and recall in predicting the high-risk category. This study presents the first real-world data on the implementation of Prosigna® in the UK, potentially optimizing future national guidelines. These findings highlight the importance of tumor grade and prognostic indices in risk stratification, offering valuable insights for personalized breast cancer management. Citation Format: Thiraviyam Elumalai, Kelly Lambert, May Teoh, Angela Rajiv, Ishtiaque Hussain, Faatimah Esmail, Aliaa Shamardal, Judith Dua, Nyan Lin Myint, Susan John, Elizabeth Bull, Saif Ahmad. Evaluating the Impact of Prosigna® Testing on Adjuvant Chemotherapy Decisions in Early-Stage ER-Positive, HER2-Negative Breast Cancer: A UK Study [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P1-10-12.

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