The polymerization of prodrug monomers also provides greater flexibility in polymer architecture, notably by allowing the design of block copolymer prodrugs with well-defined polymer prodrug blocks. Representative examples of "grafting through" systems have been mostly obtained using ring-opening metathesis polymerization (ROMP), but other studies adapted this strategy to RDRP techniques such as ATRP and RAFT. Similarly to RDRPderived polymer prodrugs obtained by the "grafting to" approach, the tumor microenvironment has been targeted by designing drug linkers sensitive to endogenous stimuli including the pH, the redox environment and the presence of specific enzymes (Table ). The additional application of an external stimulus, such as the temperature or the light, may trigger more specifically the drug release and enhance its efficiency (see 3.1 The use of endogenous stimuli