WGYRGFYC (WC8) is a peptide that selectively targets HER2 by mimicking the antigen-binding site of trastuzumab to bind specifically to HER2. Its DOTA precursor exhibits a dissociation constant (KD) of 61.20 nM for HER2. WGYRGFYC enables specific and highly sensitive detection of HER2 expression in HER2-positive breast cancer cells and tumor tissues, monitoring dynamic downregulation of HER2 expression. The compound rapidly distributes to target tissues and is efficiently cleared from non-target tissues through the kidneys, offering an optimal tumor-to-background ratio for imaging. It is a component of the PET radiotracer Ga-DOTA-WC8 and shows no significant cytotoxicity in breast cancer cells, making it suitable for non-invasive imaging diagnosis and treatment evaluation of HER2-positive breast cancer [1].