Finally, since cancer antigen 125 (CA125) is an ovarian cancer biomarker that is heavily O-glycosylated (3700 O-glycosites and 249 N-glycosites), performing and optimizing O-glycan analysis in positive ion mode on the PGC LC-MS system would be of considerable biological interest (Saldova et al., 2013). Here, MUC16 is linked to ovarian cancer.