Abstract PS2-04-25: Efficacy of maintenance endocrine therapy combined with trastuzumab + pertuzumab following taxane induction in HR+/HER2+ metastatic breast cancer: A real-world reproduction of the PATINA trial control arm

Abstract Background: The PATINA trial demonstrated that adding the CDK4/6 inhibitor palbociclib to maintenance endocrine therapy (ET) and trastuzumab ± pertuzumab significantly prolonged median progression-free survival (PFS) by approximately 15 months (HR 0.74 95% CI: 0.58-0.94). Given its potential to redefine treatment standards, our objective was to replicate and validate the control arm outcomes of the PATINA trial using real-world data. Methods: We conducted a retrospective analysis using data from the multicenter, real-world Epidemio-Strategy and Medical Economics (ESME) database, encompassing 18 French Comprehensive Cancer Centers. Eligible patients had hormone receptors-and HER2-positive (HR+)/HER2+ metastatic breast cancer (MBC), initiated first-line treatment with a taxane plus trastuzumab + pertuzumab, who did not progress after completion of chemotherapy and subsequently received maintenance therapy with trastuzumab + pertuzumab combined with endocrine therapy. Real world progression free survival (PFS) and overall survival (OS) were estimated from maintenance ET initiation in the overall cohort and in subgroups of patients. Multivariable analyses were performed including age, tumor grade, de novo MBC status, number of metastatic sites, presence of visceral metastases, and hormone receptor status (ER+/PR+ or ER+/PR-). Results: Between January 2013 and December 2023, 368 patients with HR+/HER2+ MBC who completed induction chemotherapy and transitioned to maintenance therapy with trastuzumab + pertuzumab and ET were included. The median age was 56 years (range 20-88) and most of patients had de novo MBC (67%). Prior chemotherapy +/- anti-HER2 therapy in the (neo)adjuvant setting was reported in 17.1% of patients. The median duration of taxane induction for metastatic disease was 3.9 months (range 3-7.6) and 85.6% received an aromatase inhibitor as endocrine therapy combined with trastuzumab and pertuzumab. Best response to induction therapy, a stratification factor in PATINA trial, was not recorded. After a median follow-up of 57.8 months 95% CI: 53.1-63.6, the median PFS was 28.8 months 95% CI: 22.0-33.0, with a 5-year PFS rate of 35.4% 95% CI: 29.9-40.9. The median overall survival (OS) was not reached, with 3- and 5-year OS rates of 85.2% 95% CI: 80.8-88.7 and 70.3% 95% CI: 64.3-75.5, respectively. A higher number of metastatic sites (≥3) was linked to poorer PFS adjusted HR, 95% CI: 2.07 (1.50-2.85), whereas de novo metastatic disease was associated with improved PFS adjusted HR, 95% CI: 0.75 (0.56-1.00). A sensitivity analysis performed in patients treated before 2018 (32%), i.e. before PATINA was opened to accrual, showed consistent results a median PFS of 28.1 months 95% CI: 14.9-38.7 and a 5-year OS rate of 66.6% 95% CI: 57.3-74.4. A notable difference compared to the PATINA control arm was the high rate de novo MBC in our cohort. Conclusion: In this real-world analysis, patients with HR+/HER2+ MBC treated with first-line metastatic induction chemotherapy followed by maintenance trastuzumab + pertuzumab and ET achieved outcomes in line with those reported in the control arm of the PATINA trial. Citation Format: L. Mathiot, A. Lusque, T. Grinda, T. Petit, A. Mailliez, T. Bachelot, M. Arnedos, C. Lévy, E. Brain, V. Massard, T. De La Motte Rouge, A. Goncalves, I. Desmoulins, A. Savoye, M. Leheurteur, L. Bosquet, F. Dalenc, W. Jacot, J. Frenel. Efficacy of maintenance endocrine therapy combined with trastuzumab + pertuzumab following taxane induction in HR+/HER2+ metastatic breast cancer: A real-world reproduction of the PATINA trial control arm abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS2-04-25.