Trastuzumab+pertuzumab dual HER2 blockade with endocrine therapy matches 5-year survival despite lower pCR in HR+/HER2+ eBC

Trastuzumab (HER2 mAb) plus pertuzumab (HER2 dimerization-blocking mAb) were given for 12 weeks neoadjuvantly with either endocrine therapy (ET) or weekly paclitaxel in the randomized Phase II open-label WSG TP-II trial (NCT03272477) in HR+/HER2+ early breast cancer (n=207), followed by adjuvant dual HER2 blockade in all; additional chemotherapy was mandatory for non-pCR and optional after pCR. Prior primary-endpoint data showed higher pCR with paclitaxel+HP vs ET+HP (56.4% vs 23.7%). At 5 years, OS was 100% with ET+HP vs 97.9% with paclitaxel+HP; 5-year EFS (DCIS included) was 92.1% vs 94.8%, and reported 5-year iDFS was 97.7% vs 79.8% (interpret cautiously given wide CI in the paclitaxel arm). For external context, contemporary adjuvant pertuzumab+trastuzumab+chemo yields iDFS in the mid–high 80%s at ~8 years in node-positive disease (APHINITY: 86.1% vs 81.2%; HR 0.72), while lower-risk node-negative patients treated with adjuvant paclitaxel+trastuzumab commonly see ~93% 7-year iDFS (APT).