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Changes of cell surface glycosylation are commonly seen in all types of cancers and many of these glycosylation changes result in the exposure of tumour-associated carbohydrate antigens.One of the most common glycosylation changes in epithelial cancer is the increased occurrence of the oncofetal Thomsen-Friedenreich (galactose β1, 3 N-acetylgalactosamine α-, TF) antigen, the core I structure of O-linked mucin type glycans.In normal epithelium, TF antigen is crypted and concealed by sialic acids, sulphates or by addition of other sugar chains to form branched and complex O-glycans.In cancer and pre-cancerous conditions, unsubstituted TF antigen occurs in about 90% of all human cancers.Recently we have revealed that the increased occurrence of TF antigen on the transmembrane mucin protein MUC1, a large and heavily glycosylated transmembrane mucin protein which itself is increased up to 10-folds in epithelial cancer cells, allows increased interaction of the tumour cells with a group of endogenous galactoside-binding (galectins) whose concentrations are also markedly increased in the blood of cancer patients in particular those with metastasis.We have shown that the increased interaction of cancer cells with circulating galectins in the bloodstream of cancer patients as a results of the increased expression of the cancer-associated MUC 1, the increased occurrence of the galectin-binding ligand TF on MUC 1 and the increased concentration of circulating galectins, all of which are common features in cancer, promote haematogenous spread of circulating cancer cells to remote sites.This not only provides insight into our understanding of the molecular mechanisms of cancer spreading but also has significant implication in the development of effective therapeutic strategies against metastasis and prognosis.