The PHERGain trial investigated the potential of metabolic imaging to identify candidates for chemotherapy deescalation in human epidermal growth factor receptor 2 (HER2)-positive, invasive, operable breast cancer with at least 1 breast lesion evaluable by [^(18)F]FDG PET/CT. [^(18)F]FDG PET/CT responders were defined as patients with an SUV(max) reduction (ΔSUV(max)) of at least 40% in all of their target lesions after 2 cycles of trastuzumab and pertuzumab (HP) (with or without …