Abstract PS3-11-23: Cross-country Treatment Practices after pCR Following Neoadjuvant Trastuzumab (H) and Pertuzumab (P) in HER2+ Early Breast Cancer: Preliminary Results from the PEARL-HER2 Study

Abstract Background: Pts with HER2+ early BC who achieve pCR following neoadjuvant chemotherapy (NACT) with HP routinely continue dual anti-HER2 therapy, although the added benefit of continuing HP versus H alone in this setting remains uncertain, with added cost and toxicity. PEARL-HER2 aims to clarify this question by evaluating whether adjuvant HP provides additional clinical benefit compared to H alone. Here, we report a preliminary cross-country comparison of clinical practices. Method: PEARL-HER2 is an international, retrospective cohort study including pts with HER2+ early BC who achieved pCR (ypT0/isN0) after NACT and HP. Eligible pts started NACT between Jan-2014 and Dec-2023. This descriptive analysis, data cut-off of 20-Jun-2025, summarizes diagnostic, and treatment data stratified by country. Results: Of 1045 pts screened, 649 with pCR were eligible for this analysis. Country-level characteristics are shown in Table 1. Differences in baseline characteristics included a higher proportion of pre-/perimenopausal pts in Argentina (56%), higher ER positivity in Belgium (58%) and lower Ki-67 expression in Turkey (21%). Imaging practices also differed: breast MRI was routinely used in Spain, Portugal, and Belgium, but infrequent in Turkey (15%). Staging with FDG-PET was more commonly employed in Turkey (65%) and Belgium (44%), whereas CT and bone scan were predominant elsewhere. Anthracycline-free regimens were more frequent in Argentina (100%) and Belgium (34%), contrasting with near-universal anthracycline use in Portugal and Turkey. Adjuvant HP was continued in >90% of pts in Belgium vs. <9% in Iberian countries, highlighting disparities in access. Among ER+ patients, ET use was near-universal (97%), though OFS-based combinations were infrequent even in very young pts. With a median follow-up of 44 months (IQR 29-67), only 35 relapses (5.4%) were reported, 18 (51%) of which in the central nervous system (CNS). Conclusion: This preliminary analysis reveals marked international variability in post-pCR management of HER2+ early BC. These findings should be interpreted with consideration of the unequal distribution of patients across countries, with Portugal contributing over two-thirds of the cohort. Differences in imaging and tumor burden likely reflect national screening and staging practices, while variation in adjuvant P use likely reflects national funding policies, with routine access in Belgium but limited or no reimbursement in Iberian countries. Notably, over half of reported relapses occurred in the CNS. PEARL-HER2 continues to accrue and follow patients to clarify the role of adjuvant P in this setting. Citation Format: S. Lobo-Martins, G. Gentile, H. Gouveia, N. Teixeira Tavares, M. Gonzalez-Rodriguez, E. Campôa, B. Pereira, T. Pina Cabral, E. Agostinetto, D. Cabuk, D. Alpuim Costa, F. P Duhoux, P. Mandó, T. Cunha Pereira, P. Simões, H. Wildiers, L. Arecco, R. Gerosa, C. Dauccia, S. Ramalho, M. Carvalho Couto, T. Pascual, N. Cunha, F. Sarmento, A. Martins, E. Kolemen, M. Delgado da Silva, C. van Marcke, S. Rivero, A. Garcia, G. Nader-Marta, M. Piccart, P. Kristanto, E. de Azambuja. Cross-country Treatment Practices after pCR Following Neoadjuvant Trastuzumab (H) and Pertuzumab (P) in HER2+ Early Breast Cancer: Preliminary Results from the PEARL-HER2 Study [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 PS3-11-23.