A pharmaceutical composition comprising a camptothecin as active ingredient is herein described. In particular immediate-release therapeutic systems are described for the improved oral absorption of 7-[(E)-t-butyloxyminomethyl] camptothecin, comprising a matrix consisting of liquid amphiphilic substances or having a melting point lower than 60° C., in which the active principle is at least partially dissolved and/or dispersed and/or inglobated.