However, in in vivo transfection, both LP-HAPC-2mol%PEG2000 and LP-HAPC-2mol%FA-PEG2000 lipoplexes with PLK1 siRNA inhibited tumor growth compared with Cont siRNA, indicating that the in vivo anti-tumor effect of PEG-modified siRNA lipoplexes was not correlated with the in vitro one. The gene discussed is PLK1; the disease is neoplasm.