MRC1 and breast cancer: Extrapolating from our still-ongoing clinical trials with a 68Ga-labeled anti–human epidermal growth factor receptor 2 single-domain antibody breast cancer PET tracer (26) and an anti-CD206 single-domain antibody macrophage PET tracer (25), we are hopeful that the future clinical anti-LAG-3 single-domain antibody PET tracer will also be safe and sensitive and will conveniently provide a whole-body picture of LAG-3 expression levels in a same-day imaging procedure with acceptable dosimetry levels.