Pharmaceutical compositions comprising a nucleic acid and a gene delivery polymer for the treatment of mammalian cancer or hyperproliferative disorders and methods of using thereof for the treatment of mammalian cancer or hyperproliferative disorders by intratumoral, intraperitoneal or systemic injection. IL-12 gene is transferred to various tumours using PPC (polyethylene glycol (PEG) - polyethylenimine (PEI) - cholesterol) soluble lipopolymers.