Phesgo 1200 mg / 600 mg Phesgo 1200 mg/600 mg contains Pertuzumab 1200 mg and Trastuzumab 600 mg, two targeted medicines used together for the treatment of HER2-positive breast cancer. They work by attaching to the HER2 protein on cancer cells and blocking the signals that encourage these cells to grow and survive. Combining the two medicines provides a stronger targeted approach against HER2-driven cancer. The 1200 mg/600 mg strength is used as the initial loading dose and is administered as a subcutaneous injection by a healthcare professional.