Abstract PO3-05-02: Impact of hormone receptor expression level in HR+/HER2- metastatic breast cancer in the large French ESME cohort

Abstract Background: In patients (pts) with early breast cancer (BC), the level of expression of estrogen receptor (ER) evaluated by immunohistochemistry is prognostic and predictive while progesterone receptor (PR) expression has an additional prognostic value. Allred scoring combines the percentage of positive cells and the intensity of staining. It is widely used for treatment choice for early BC. In metastatic setting, its role is less defined. Methods: The ESME database is a French National cohort of all consecutive pts who initiated a first-line treatment for metastatic BC (MBC) between January 2008 and December 2020 in one of the 18 French Comprehensive Cancer Centers (NCT03275311). For this study, we selected pts with HER2- MBC, known ER expression and intensity percentages, known PR status and who received endocrine-based therapy as first-line metastatic treatment. Primary objective was to evaluate the overall survival (OS) and first line progression-free survival (PFS1) under endocrine therapy according to ER and PR expression level. ER expression was defined using Allred score on the last available tumor sample. PR status was defined using a positive (≥10%)vs negative ( < 10%) threshold. Secondary objective was to evaluate clinical PFS1 whether de novo or recurrent MBC and according to type of first line therapy (mono- vs combined endocrine therapy). Results: In the ER+ ± PR+/HER2- population, 8269 pts had information on ER percentage and staining intensity. Median follow-up was 53.4 months (95%CI [51.9; 54.7]). Allred score distribution, OS and PFS1 are described in table 1. Median OS was 43.1 months [41.1; 45.0] for the PR- group compared with 52.3 months [50.5; 54.4] for the PR+ group. After adjustments, patients with a PR- tumour had still a worse prognosis (HR=1.20, 95%CI [1.12-1.28], p<0.001). Median PFS1 was 10.2 months[9.6; 10.8]and 14.8 months[14.2; 15.4] for pts with PR- vs PR+ tumour (HR=1.36 (1.29-1.43), p<0.001) and PR status remained significant prognostic factor independently of de novo or recurrent status and association or not with a targeted therapy. Conclusion: ER expression evaluated using the Allred scoring, as well as PR positivity, retain prognostic value in first-line MBC patients. Table 1 : OS and PFS according to Allred status, de novo status and type of endocrine therapy. * Selected variables on multivariate model include PR status, age, SBR grade, histological subtype, number of metastatic site, type of metastasis (non visceral, visceral, brain visceral), HER 2 (0 vs 1-2), metastatic-free interval, mono- vs combined endocrine therapy. Citation Format: Marie Alexandre, Florence Castan, Thibault De La Motte Rouge, Audrey Mailliez, Etienne Brain, Thomas Bachelot, Monica Arnedos, Florence Dalenc, Jean-Marc Ferrero, Vincent Massard, Isabelle Desmoulins, Marie-Ange Mouret-Reynier, Christelle Levy, Anthony Gonçalves, Anca Berghian, Aude-marie Savoye, Jean-Sébastien frenel, Lise Bosquet, Suzette Delaloge, William Jacot. Impact of hormone receptor expression level in HR+/HER2- metastatic breast cancer in the large French ESME cohort [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 PO3-05-02.