ERBB2 and breast cancer: D’Huyvetter et al. (2021) reported the results of a phase I clinical trial with 131I GMIB-Anti-HER2-VHH1 in six healthy volunteers and three breast cancer patients. VHH1 is a single-domain antibody covalently linked to therapeutic 131I via the linker SGMIB (succinymidil-4-guanidino-methyl-3-iodobenzoate). Its favorable toxicity profile, with an absorbed dose to the kidney of 1.54 ± 0.25 mGy/MBq, and positive uptake in metastatic lesions, offers new therapeutic options for patients who have progressed on trastuzumab, pertuzumab, and trastuzumab emtansine (D’Huyvetter et al., 2021).