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). This evidence concerns the gene ERBB2 and breast carcinoma.