This study evaluates the safety, biodistribution, and dosimetry of 89Zr-site-specific (ss)-pertuzumab PET in patients with HER2-positive breast cancer. Six patients received 74 MBq of 89Zr-ss-pertuzumab and underwent PET/CT at various time points post-administration. The results showed that 89Zr-ss-pertuzumab was safe, with no toxicities observed. The optimal imaging time point was 5–8 days after administration, and the radioimmunoconjugate successfully detected known sites of malignancy, indicating HER2 positivity. The average effective dose for 89Zr-ss-pertuzumab was 0.54 ± 0.03 mSv/MBq, comparable to other HER2-targeted PET tracers. The study concluded that 89Zr-ss-pertuzumab has potential clinical applications, including real-time evaluation of HER2 status to guide biopsy and treatment decisions.This study evaluates the safety, biodistribution, and dosimetry of 89Zr-site-specific (ss)-pertuzumab PET in patients with HER2-positive breast cancer. Six patients received 74 MBq of 89Zr-ss-pertuzumab and underwent PET/CT at various time points post-administration. The results showed that 89Zr-ss-pertuzumab was safe, with no toxicities observed. The optimal imaging time point was 5–8 days after administration, and the radioimmunoconjugate successfully detected known sites of malignancy, indicating HER2 positivity. The average effective dose for 89Zr-ss-pertuzumab was 0.54 ± 0.03 mSv/MBq, comparable to other HER2-targeted PET tracers. The study concluded that 89Zr-ss-pertuzumab has potential clinical applications, including real-time evaluation of HER2 status to guide biopsy and treatment decisions.