ERBB2 and cancer: Therefore, we generated sdAbs that bind LAG-3, as sdAbs are small-sized antibody fragments that allow rapid generation of high contrast images of molecular markers expressed on cancer cells and cancer-infiltrating immune cells without toxicity or evidence of immune responses against the sdAb-based tracer [47], as shown in clinical trials using sdAbs for PET imaging of HER2 [33] and MMR [34].