The cancer-associated mucin MUC1, decorated with N-acetylgalactosamine (GalNAc) linked to serine or threonine residues (known as the Tn antigen; Tn-MUC1), is frequently found in solid tumors such as pancreatic cancer and has become a target for several therapeutic strategies, including CAR-T cell therapy23–31. The gene discussed is MUC1; the disease is cancer.