Anti-MUC1and anti-Tn antibodies have long been used clinically in cancer diagnosisand therapy.24,45 Initial efforts were focusedon IgG1 antibodies that block MUC1 on the surface of cancer cells.However, anti-MUC1 antibodies have also been conjugated to radioisotopesto use in both imaging and cancer therapy, as well as to small-moleculetoxins, resulting in antibody–drug conjugates (ADCs) approvedfor the treatment of various cancers, including trastuzumab emtansine,brentuximab vedotin, and gemtuzumab ozogamicin. Here, MUC1 is linked to cancer.