MUC1 and plasma cell myeloma: An early example of O-glycosylation in immunotherapy is provided by mucin 1 (MUC1), a transmembrane glycoprotein overexpressed and abnormally glycosylated with Tn and sialyl Tn antigen in adenocarcinomas, squamous cell carcinomas, and myelomas making it a broad based cancer biomarker (127–129).