Method of treating cancer

A method for treating a cancer selected from the group consisting of a cancer characterized by EGFR-overexpressing cells, a cancer characterized by HER2-overexpressing cells and prostate cancer,

• said method comprising administering to a subject in need thereof a polyplex of a double stranded RNA (dsRNA) and a polymeric conjugate, wherein said polymeric conjugate consists of a linear polyethyleneimine (LPEI) covalently linked to one or more polyethylene glycol (PEG) moieties, each PEG moiety being conjugated via a linker to a targeting moiety capable of binding to a cancer antigen,
• wherein said linker forms an —S—S—, NH—CO—, —CO—NH—, —S—C—, O—CO—, —CO—O— or urea (—NH—CO—NH) bond with said targeting moiety, and
• wherein said linker is a peptide moiety;
• wherein said peptide moiety is —(NH—(CH2)7—CO)-Phe-Gly-Trp-Trp-Gly-Cys- (SEQ ID NO:
• 2) or —(NH—(CH2)7—CO)-Phe-Phe-(NH—CH2—CH(NH2)—CO)-Asp-Cys- (SEQ ID NO:
• 3).