Micelles and vesicles have long been proposed as carriers for low molecular weight molecules including drugs.The ability of micelles to deliver drug is usually tested by incubating them with a monolayer of cell.This assay does not take the actual structure of tumors into account,since it neglects the necessary penetration of particles into the tissue.Multicellular tumor spheroids (MCTS)can act as a 3D tumor model to investigate the biological responses to polymeric micelles.