Tucatinib (HER2 TKI) + trastuzumab/pertuzumab extends PFS as 1L HER2+ MBC maintenance—benefit holds across HR/BM subgroups

Tucatinib (TUC), an oral HER2-selective tyrosine kinase inhibitor, was evaluated in the Phase 3 HER2CLIMB-05 maintenance trial (NCT05132582) after induction taxane + trastuzumab/pertuzumab (HP) in HER2+ metastatic breast cancer (TUC+HP n=326; PBO+HP n=328; cutoff Sep 5, 2025). Investigator-assessed median PFS improved from 16.3 to 24.9 months (HR 0.641, p<0.0001), with consistent subgroup separation: de novo 28.9 vs 16.8 months; recurrent 21.3 vs 12.7 months; HR+ 25.0 vs 18.1 months; HR− 24.9 vs 12.6 months; baseline brain metastases 8.5 vs 4.2 months. Confirmed ORR was also higher overall (22.6% vs 15.2%) and in each stratified subgroup (e.g., BM yes 15.0% vs 8.3%), and safety by subgroup was described as consistent with the overall population with no new safety signals; as a benchmark, historical 1L THP (CLEOPATRA era) delivered median PFS ~18.5–18.7 months, while 1L trastuzumab deruxtecan + pertuzumab (approved Dec 15, 2025) reported median PFS 40.7 months vs 26.9 months for THP, suggesting tucatinib maintenance is an incremental add-on to HP rather than a new “best-in-class” 1L anchor regimen.