Among the 65 anti-HER2 FLAP candidates created, three bind to the same epitope as the parental mAb, and their KD values are within a clinically relevant range that binds to high HER2-expressing cells but reduces on-target off-tumour binding risk, demonstrating that our strategy is a promising method to develop small antibody mimetics that could contribute to molecular-targeted therapy and diagnosis. Here, ERBB2 is linked to neoplasm.