The latest trends of drug development are focused on such drug forms that enable targeted therapy of a biologically active substance, preferentially at the site of the required therapeutic effect. Target effect drugs are primarily utilized in such areas where side effects of the active component may potentially cause damage to any healthy parts of the body. This danger is most relevant in cytostatic therapy. Polymeric substances, especially water-soluble polymers, used as drug carriers offer an important possibility of solving the problem. The attachment of a cytostatic to a water-soluble polymer through a chemical bond enables significant increase in solubility of insoluble or slightly soluble drugs, substantially decreasing their toxicity. The high molecular weight of polymers protects the drug from a quick elimination from the body by glomerular filtration enabling an extended circulation in the blood, as well as greater biological efficiency of the drug. Besides, macromolecular substances, especially synthetic polymers, may accumulate in solid tumors due to the EPR (enhanced permeability and retention) effect [Maeda 2000, 2001]. If a cancerostatic is bound to a macromolecular carrier, this fact may be used for its targeted accumulation in the tumor. A great number of systems that are based on this principle have been developed. Polymeric micelles are one of them. They represent a carrier system which is structurally different from soluble polymers developed to achieve tumor specific transport of cytostatics to solid tumors, they also take advantage of the EPR effect of firm tumors to increase accumulation of the macromolecular drug in the tumor but they are usually prepared by arranging amphiphilic diblock copolymers into macromolecular micellic formations creating colloid solutions. In the micelles, the drug is usually bound to the micellic hydrophobic core by physical (hydrophobic interactions, ionic bonds) or covalent bonds [Kataoka 2001, Yokoyama 1999, Bae 2003, Yoo 2002, Bronich 1999]. If the drug is to be released from the micelle the chemical bond needs to be broken and, at the same time, the hydrophobic interactions in the micellic core disintegrated. This is especially true for hydrophobic drugs. On the other hand, in soluble systems that accumulate in solids tumors the macromolecules are dissolved in the aqueous environment on a molecular basis and the molecule usually takes the shape of a random coil. The drug is then in contact with a hydrophilic polymer and to be released it does not have to overcome the barrier of hydrophobic interactions. Polymeric conjugates of cancerostatics with soluble polymers have been prepared and studied in which the drug with an anticancer effect was bound to the polymer by a non-cleavable covalent bond, hydrolytically unstable ionic bond or by a covalent bond susceptible to enzymatic or simple chemical hydrolysis. Such systems are capable of releasing the cancerostatic from the carrier in its active form either in the tumor or, more specifically, directly in the tumor cell. A significant group of such drugs is formed by polymeric drugs based on copolymers of N-(2-hydroxypropyl)methacrylamide (HPMA), a number of which is actively targeted to tumors through a directing structure attached to the polymer (antibodies, hormones) [Duncan 1985, Rihova 2000, Kopecek 2001, 2000]. However, their synthesis is rather complicated. References quote much information on the preparation and studies of properties of polymers carrying a cancerostatic attached to the polymer by a bond susceptible to hydrolysis in an aqueous environment. [Kratz 1999]. A significant role among them is also played by HPMA copolymers carrying the doxorubicin cancerostatic bound to the polymeric chain by a hydrolytically cleavable hydrazone bond [Etrych 2002, Ulbrich 2004a, Ulbrich 2004b, Ulbrich—patents]. This bond is relatively stable in the bloodstream environment (during the transport in the body) and hydrolytically unstable in a slightly acid environment of a living cell. The rate of hydrolysis of this bond controls the rate of drug release and whence the concentration of the active substance at the site of required effect. Both in vitro and in vivo tests in mice revealed that these polymeric cancerostatics showed significantly higher anticancer effect against a number of tumor lines in comparison with a free drug and in a number of cases their application resulted in a total cure of tested animals even in a therapeutic mode of administration [Rihova 2001, Etrych 2001]. The major problem associated with the application of HPMA copolymers is their non-cleavable carbon chain; therefore the area of molecular weights that can be used for the preparation of the polymeric carrier is limited to molecular weights smaller than 40,000 to 50,000, i.e. below the exclusion limit of the body. Polymers of a higher molecular weight cannot be effectively and sufficiently eliminated from the body and their application would lead to their excessive accumulation in the body. To achieve an efficient EPR effect, i.e. significant accumulation in tumors, polymers, including HPMA copolymers, with a molecular weight high above the exclusion limit need to be used (Seymour 1995, Noguchi 1998). Therefore, it is convenient for the molecular weight of the polymeric carrier to be high enough but, at the same time, to ensure for the degradation of the polymer after the active component is released into fragments that can be excluded from the body by, e.g. glomerular filtration. This invention suggests and demonstrates the efficiency of a macromolecular polymeric drug with a defined and biodegradable carrier skeleton that allows for the transport of the cytostatic into the tumor as well as subsequent exclusion of the polymeric carrier from the body.