Polymeric carriers may deliver therapeutic substances and biomolecules to the destination place in unchanged form. Their use in the therapy of solid tumors in comparison to unbound drugs brings about several benefits, such as drug dose reduction as well as adverse effects decrease. The primary advantage of the described conjugates is the control release of the pharmacologically or biologically active substance, by means of the use of proper chemical bonds between constituents of drug delivery system (DDS). The system may be transported in an organism in two ways: passively, by using the enhanced permeability and retention (EPR) effect, or actively, by placing on its surface a molecule which selectively creates the way to its destination. To elaborate such a DDS type requires the knowledge of the biological nature of neoplastic tumor and the chemical properties of the carrier and the therapeutic substance or biomolecule.