FIELD : medicine; pharmaceuticals.SUBSTANCE : invention refers to pharmaceutics, namely to a pharmaceutical composition for treating and/or preventing a malignant tumour. Composition contains as an active ingredient an antibody or its fragment with immunological reactivity with respect to protein CSPG5 or its fragment, consisting of at least 7 or more consecutive amino acid residues, where the CSPG5 protein consists of any of the amino acid sequences presented by SEQ ID NO : 8, 4, 6, 10 and 12, or amino acid sequence with amino acid identity with these amino acid sequences 80? or more.EFFECT : invention provides the possibility of creating a composition effective for treating and/or preventing a malignant tumour.4 cl, 5 dwg, 7 ex