Abstract PO3-01-09: Results of a prospective observational study evaluating the impact of the Prosigna assay on neoadjuvant treatment decision-making in patients with early-stage HR+/HER2- breast cancer

Abstract Background. Prosigna (PAM50) is an FDA-approved prognostic test that measures the expression of 50 classifier genes in breast cancer tissue samples. It provides intrinsic subtyping, which classifies the biology of an individual patient's tumor, as well as a risk of recurrence (ROR) score that predicts the probability of distant recurrence over 10 years. Currently, the Prosigna assay is only approved for use in postoperative specimens. Given studies demonstrating that Prosigna can identify tumors that are more likely to benefit from chemotherapy, this decision-impact study sought to evaluate whether the assay could influence physicians' choices and patients' confidence in the neoadjuvant treatment plan. Methods. This prospective observational study was conducted at a single institution and included patients with HR+/HER2- breast cancer measuring ≥ 0.5 cm, any nodal status, who were deemed candidates for neoadjuvant systemic treatment based on physician’s choice. Formalin-fixed paraffin-embedded core biopsy specimens were centrally analyzed using Prosigna. Patients' tumors were classified according to intrinsic tumor subtype (Luminal A, Luminal B, HER2-enriched, Basal-like) and ROR score (low, intermediate, or high). Physicians and patients were surveyed before and after performing Prosigna, regarding neoadjuvant therapy recommendations. The primary endpoint was assessment of the effect of Prosigna on oncologists' treatment recommendations and the actual treatment received (neoadjuvant hormonal therapy NAHT, neoadjuvant chemotherapy NACT, or upfront surgery). Secondary endpoints included determining whether treatment changes were based on ROR score, intrinsic subtype, or both, as well as assessing physicians' and patients' confidence in the treatment plan. Results. A total of 54 patients were enrolled in the study between March 2019 and April 2023. The distribution of intrinsic tumor subtypes was as follows: 15 patients (28%) had a Luminal A subtype, 34 (63%) had a Luminal B subtype, 3 (6%) had a HER2-enriched subtype, and 2 (4%) had a Basal-like subtype. Thirty-three patients (61%) were classified as ROR-low, 11 (20%) as ROR-intermediate, and 10 (19%) as ROR-high. Out of the 43 patients who had both pre- and post-assay survey results available, a change in the treatment decision was observed in 28% of cases. Specifically, 14% of patients transitioned from NAHT to NACT, 7% from NACT to NAHT, and 5% from NACT to upfront surgery, as shown in the Table. Treatment changes were based on the ROR score, intrinsic subtype, and both in 33%, 3%, and 64% of cases, respectively. Overall, 45% of physicians experienced an increase in confidence for the treatment plan after Prosigna testing, while 16% reported a decrease and 39% maintained the same level of confidence. Sixty-two percent of patients experienced a reduction in anxiety about treatment. Associations of ROR score and intrinsic subtypes will be presented at the meeting. Conclusion. Prosigna performed on presurgical core biopsies influenced oncologists' treatment recommendations regarding neoadjuvant treatment and reduced patient anxiety about treatment among patients with early-stage HR+/HER2- breast cancer. Table. Neoadjuvant treatment recommendations before and after Prosigna assay, overall and according to nodal status. Data are presented as frequencies (%). Abbreviations: NACT, neoadjuvant chemotherapy; NAHT, neoadjuvant hormonal therapy. Citation Format: Chiara Corti, Xiangying Chu, Pedro Exman, Danielle Kline, Nolan Priedigkeit, Nabihah Tayob, Erica Mayer, Adrienne Waks, Melissa Hughes, Antonio Giordano, Giuseppe Curigliano, Nancy Lin, Tari King, Rinath Jeselsohn, Deborah Dillon, Elizabeth Mittendorf, Sara Tolaney. Results of a prospective observational study evaluating the impact of the Prosigna assay on neoadjuvant treatment decision-making in patients with early-stage HR+/HER2- breast cancer abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-01-09.