International variation in diagnostic and treatment practices in patients with HER2+ EBC: The RWE PEARL-HER2 study.

517 Background: Pts with HER2+ EBC achieving pCR post neoadjuvant chemotherapy (NACT) with trastuzumab (H) and pertuzumab (P) show favorable outcomes. Yet, management varies widely within healthcare systems, including access to continuation of adjuvant (adj) P. We compared diagnostic and treatment practices across countries. Methods: PEARL-HER2 is an international retrospective real-world cohort including pts with HER2+ EBC achieving pCR (ypT0/isN0) after NACT-HP (Jan 2014 to Dec 2023). This descriptive preliminary analysis (data cut-off Jan-2026) summarizes diagnostic and treatment data stratified by country. Results: 1345 pts with pCR were included. Significant heterogeneity in pts and disease characteristics was observed (Table 1). Diagnostic methods also varied: use of breast MRI ranged from 11-97% across countries (>85% in Spain/Portugal; Peru, 11%), while FDG-PET/CT ranged from 0-72% (overall 20%; Turkey, 72%; p<0.001). Anthracycline-based NACT varied from <20% in Argentina and Brazil to >85% in Portugal and Turkey (p<0.001). Adj P was administered to 33% of pts overall (0-97%; p<0.001), with high use in countries with public reimbursement and minimal in those without. Among ER+ pts, ET use was uniformly high (98%; p=0.590), but regimen selection varied substantially (p<0.001): tamoxifen (42%) and aromatase inhibitor (58%). Events occurred in 6% of pts (invasive/non-invasive relapses and death); median FU was 40 months (IQR 24–62). Conclusions: This analysis indicates marked cross-country variability in management of HER2+ EBC. Use of adj P closely aligned with national reimbursement policies, highlighting access as a major determinant of care beyond clinical risk and guideline recommendations. Characteristics Argentina (N=155) Belgium (N=217) Brazil (N=107) Italy (N=52) Peru (N=18) Portugal (N=603) Spain (N=110) Turkey (N=83) Total (N=1345) P-value Age, median (IQR) 47 (41–56) 54 (45–63) 46 (40–52) 53 (45–61) 45 (41–56) 52 (45–62) 53 (44–59) 51 (45–61) 51 (43–61) <0.001 Pre-/perimenop., n (%) 96 (62) 91 (43) 72 (72) 26 (50) 13 (72) 286 (48) 52 (48) 38 (46) 674 (51) <0.001 NST histology, n (%) 145 (95) 197 (91) 89 (83) 48 (94) 18 (100) 558 (93) 103 (95) 83 (100) 1241 (93) <0.001 ER–, n (%) 77 (50) 95 (44) 61 (58) 16 (31) 5 (28) 277 (46) 57 (52) 44 (53) 632 (47) <0.001 cN0, n (%) 58 (37) 28 (13) 43 (40) 24 (46) 2 (11) 267 (44) 50 (46) 21 (25) 493 (37) <0.001 Breast MRI | PET-CT, n (%) 123 (80) | 14 (9) 126 (58) | 63 (29) 73 (71) | 27 (26) 13 (25) | 13 (25) 2 (11) | 0 (0) 521 (86) | 70 (12) 102 (97) | 21 (19) 35 (42) | 60 (72) 995 (75) | 268 (20) <0.001 | <0.001 Anthracycline-based NACT, n (%) 19 (12)</