N-glycolylneuraminic acid as a carbohydrate cancer biomarker

•Aberrant glycosylation is a well-known hallmark of human tumors, and one of the forms of aberrant glycosylation in human tumors is the expression of Neu5Gc.•Neu5Gc-containing antigens as a class of cancer biomarkers have been under-explored for cancer diagnosis, monitoring and prognosis.•The mechanism and source of Neu5Gc expressed by human tumors remains to be clarified.•The emerging hypothesis of cancer cell-generated Neu5Gc provides a rationale for the use of Neu5Gc as a universal cancer biomarker.