Use of N-[2-(2,1,3-benzothiadiazol-5-ylamino)-6-(2,6 dichlorophenyl)pyrido[2,3-d]pyrimidin-7-yl]-N-(1,1-dimethylethyl)-urea (I) and its hydrates, salts or solvates, for the preparation of medicament to treat leukemia and myeloids leukemia, is claimed. ACTIVITY : Cytostatic. The anti-tumor activity of (I) was tested in severe combined immunodeficient mice CB-17. The result showed that (I) exhibited tumor mass reduction of 80%. MECHANISM OF ACTION : None given.