Pembrolizumab (PD-1) added to neoadjuvant THP trends toward higher 3-year EFS in stage II–III HER2+ breast cancer

In the randomized Phase 2 neoHIP trial (NCT03747120), patients with stage II–III HER2-positive breast cancer received neoadjuvant paclitaxel + trastuzumab + pertuzumab (THP) with or without pembrolizumab (an anti–PD-1 checkpoint inhibitor), with prior reporting of higher pCR for THP–pembro vs THP (67% vs 48%, p=0.026). With 37 months median follow-up and a January 23, 2026 data cutoff, 36-month EFS was 100% (95% CI, 100–100) with THP–pembro vs 95% (95% CI, 89–100) with THP (n=116; 58/arm; p=0.099), with 3 EFS events all in the THP arm and 2/3 events occurring in non-pCR patients. While cross-trial comparisons are imperfect (and this study is underpowered for EFS), the control-arm 3-year EFS of 95% is broadly in-family with contemporary dual HER2 blockade regimens in early disease (e.g., adjuvant pertuzumab+trastuzumab chemo in APHINITY: node-positive 3-year iDFS 92.0% vs 90.2%; neoadjuvant TCHP in KRISTINE: 3-year EFS 94.2%).