Glycans are "covalent assemblies of sugars (oligosaccharides and polysaccharides) that exist in either free form or in covalent complexes with proteins or lipids (glycoconjugates)."

To quote Fuster and Esko 2005: "A growing body of evidence supports crucial roles for glycans at various pathophysiological steps of tumour progression.  Glycans regulate tumour proliferation, invasion, haematogenous metastasis and angiogenesis, and increased understanding of these roles sets the stage for developing pharmaceutical agents that target these molecules.  Such novel agents might be used alone or in combination with operative and/or chemoradiation strategies for treating cancer."

Key points summarized in their paper are as follows (quoting directly):

• "Tumours aberrantly express various glycans.  Glycans regulate many different aspects of tumour progression, including proliferation, invasion, angiogenesis and metastasis.
• The proliferation of tumour cells is potentiated by the ability of glycoproteins and glycosphingolipids to directly activate growth-factor receptor tyrosine kinases and by the ability of proteoglycans to function as co-receptors for soluble tumour growth factors.
• The overexpression of specific glycosyltransferases by tumour cells promotes the formation of tumour glycans that facilitate invasion.
• Carcinomas commonly overexpress O-linked glycans in the form of cell-surface and secreted mucins that present ligands for adhesion receptors, such as the selectins, which promote the ability of tumour cells to interact with host platelets, leukocytes and endothelial cells.  These interactions facilitate haematogenous metastasis of tumour cells.
• Glycosphingolipids, in the form of gangliosides, are overexpressed by a range of tumours, and their shedding into the bloodstream might impair host immunity to some tumours.
• During tumour proliferation and invasion, heparan-sulphate proteoglycans (HSPGs) that are present on the surface of tumour cells function as co-receptors to stabilize growth-factor receptor signalling complexes.  Secreted HSPGs that are present in the extracellular matrix store growth factors that can be mobilized by the action of tumour heparanases.  A similar mechanism that involves endothelialassociated HSPGs and endothelial growth factors facilitates vascular sprouting during tumour angiogenesis.
• Some glycans can be measured in the bloodstream, and their use as markers of disease burden can be used to screen for specific cancers as well as track response to therapy.
• Experiments in which glycan function is genetically altered in cell-culture systems or mouse tumour models validate their potential as targets for anticancer therapy.
• A few glycan-based targeting strategies are currently being tested in clinical trials.  As we learn more about the roles of glycans in tumour progression, new targets will continue to emerge for drug design."

Although not discussed in the above paper, note that the active compounds in medicinal mushrooms such as Trametes versicolor (formerly Coriolus versicolor) and Grifola frondosa (Maitake) tend to be glycans.  These mushrooms and active compounds are widely prescribed in Asia for cancer treatment on the basis of extensive research and clinical experience.  See Section 3.2 of this website and Ferguson 2007 for further information.