Using a human epidermal growth factor receptor 2 (HER2) breast cancer model, Lewis et al.[164] covalently coupled a strained norbornene (dienophile) to a well characterized anti‐HER2 antibody trastuzumab followed by treatment with tetrazine substrates bearing radioisotopes 64Cu and 89Zr. Here, ERBB2 is linked to breast carcinoma.