Glycopeptides as a Tool for Early Detection of Cancer.

Protein glycosylation, as one of the most common and complex posttranslational modifications, plays an important role in many biological processes. Along with the intensive progress in MS techniques and development of glycan search tools and databases, glycoproteomics has become a popular subject of studies. The possibility of simultaneous identification of amino acid sequence, glycosylation sites, and glycan composition enabled the monitoring of changes in glycosylation patterns in various pathological states. In this issue, Saraswat et al. describe MS-based investigations of glycopeptide changes in oral cavity squamous cell carcinoma (OSCC). Their findings indicate glycopeptides with changed expression levels and the presence of altered glycan forms observed in four proteins derived from OSCC patients' sera. Proteins carrying this distinctive pattern are in the group of the most abundant components of serum, IgG1, IgG4, HPT, and TRFE, which makes their identification more accessible. Described changes, characteristic for cancer serum samples, may be considered as potential diagnostic indicators of OSCC; however, there is still a need to establish a universal glycopeptide-based biomarkers database, where all glycoproteomic data can be collected from all types of cancer studies and evaluated using meta-analyses. Only then, early diagnosis of patients using MS-based approach will make sense, as those investigations are very convoluted, and all efforts made during sample preparation and analysis will pay off when comprehensive anticancer prevention will be achieved during single measurement.