Different types of nanovectors: a) First-generation nanovectors (e.g. currently clinical liposomes) comprise a container and an active principle. They localize in the tumor by Enhanced Permeation and Retention (EPR), or the enhanced permeability of the tumor neovasculature; b) Second-generation nanovectors further possess the ability for the targeting of their therapeutic action via antibodies and other biomolecules, remote activation, or responsiveness to environment; c) Third-generation nanovectors such as multistage agents are capable of more complex functions, such a time-controlled deployment of multiple waves of active NPs, deployed across different biological barriers and with different sub-cellular targets. Reprinted by permission from Macmillan Publishers Ltd.[58]