Although the tumor microenvironment provides access to different stimuli (e.g., acidic pH, higher concentration of certain enzymes, reducing environment) that can be exploited, polymer prodrugs nanocarriers from the "grafting to" approach have also been designed to be sensitive to both endogenous et exogenous stimuli (Table ). This was achieved to improve their biological performances and tackle some potential limitations associated with the use of one unique stimulus (e.g., lack of selectivity).