Cancer-associated glycosphingolipids have been used as markers for diagnosis and targets for immunotherapy of malignant tumors. Recent progress in the analysis of their implications in the malignant properties of cancer cells revealed that cancer-associated glycosphingolipids are not only tumor markers, but also functional molecules regulating various signals introduced by membrane microdomains, lipid rafts. In particular, a novel approach, enzyme-mediated activation of radical sources combined with mass spectrometry, has enabled us to clarify the mechanisms by which cancer-associated glycosphingolipids regulate cell signals based on the interaction with membrane molecules and formation of molecular complexes on the cell surface. Novel findings obtained from these approaches are now providing us with insights into the development of new anticancer therapies targeting membrane molecular complexes consisting of cancer-associated glycolipids and their associated membrane molecules. Thus, a new era of cancer-associated glycosphingolipids has now begun
