Pembrolizumab, Pertuzumab, Trastuzumab combination

The combination of pembrolizumab, pertuzumab, and trastuzumab is an investigational treatment regimen primarily being studied for HER2-positive breast cancer. This combination brings together immune checkpoint inhibition (pembrolizumab) with dual HER2-targeted therapy (pertuzumab and trastuzumab). ## Mechanism of Action This combination therapy works through multiple mechanisms: 1. **Pembrolizumab (Keytruda)** is a PD-1 blocking antibody that helps restore anti-tumor immune responses by preventing the interaction between PD-1 on T cells and its ligands on tumor cells[7]. 2. **Pertuzumab (Perjeta)** is a HER2-targeted monoclonal antibody that binds to subdomain II of the HER2 receptor, preventing HER2/HER3 heterodimerization and homodimerization[5]. 3. **Trastuzumab** is a HER2-targeted monoclonal antibody that binds to a different domain of HER2 than pertuzumab, locking onto HER2 on cancer cells to stop them from growing and kill them[3][5]. ## Clinical Development The combination is being investigated in clinical trials for HER2-positive breast cancer: - The Keyriched-1 trial (NCT03988036) is studying this regimen in HER2-enriched early breast cancer. In this trial, 48 patients with HER2 2+ (ISH+) or 3+ early breast cancer received pembrolizumab (200 mg), trastuzumab biosimilar, and pertuzumab every 3 weeks for 12 weeks[8]. - Another phase Ib study has investigated pembrolizumab in combination with trastuzumab emtansine (T-DM1) in metastatic HER2-positive breast cancer, showing it was a safe and tolerable regimen[2]. The rationale for this combination is based on the high efficacy of anti-HER2 agents and the potentially high immunogenicity and immune checkpoint protein expression in HER2-enriched early breast cancer[8].