Objective: tumor. Strategies of drug targeting at the tumor mass level.

Concurrent with the development of new antitumor drugs, there is intensive research to develop strategies and systems to optimize the efficacy of well-known anticancer agents. The main research lines are: (a) reduction in toxicity, (b) improvement of administration and (c) overcoming drug resistance. Drug targeting systems allow us to act on these three points. The best way to increase efficacy and reduce toxicity of an anticancer agent is targeting the drug at the level of the tumor masses and maintaining its concentration there for enough time to optimize its therapeutic action. Numerous strategies have been developed to achieve this second order targeting, based on the use of polymeric-drug conjugates, polymeric micelles, liposomes and albumin conjugates and nanoparticles, whose main features of toxicity, efficacy and administration are discussed in this review.