The present inventors have demonstrated that circulating auto-antibodies to cancer antigens hold promise as specific and sensitive biomarkers for the early detection of cancer. The present invention thus relates to methods of detecting cancer in a sample, comprising utilizing a glycopeptide bait derived from human mucins with different cancer-associated O-glycans. Detected antibodies were demonstrated as glycopeptide specific, and it could be discriminated between e.g. colorectal cancer patients and healthy individuals. The inventors have also developed monoclonal antibodies based on the identified glycopeptides epitope baits, and demonstrated differential expression of the relevant target antigens. The invention thus, in a lock and key-based manner includes both glycopeptides and antibody tools for early detection of cancer, as well as methods of using the same for in situ visualization and treatment of specific cancer types.