A plasmid DNA cancer vaccine encoding the tumor-associated antigen (TAA) human epidermal growth factor receptor type-3 (HER-3; HER3), with potential antineoplastic and immunomodulating activities. Upon intramuscular administration of the plasmid DNA vaccine pING-hHER3FL and after cellular uptake by muscle cells, the plasmid DNA expresses HER-3 which, may elicit both antigen-specific cytotoxic T-lymphocyte (CTL) and humoral immune responses against tumor cells expressing HER-3. HER-3 plays a key role in tumor cell proliferation and its overexpression is associated with poor prognosis. HER-3 is associated with tumor cell resistance to anti-HER-2 therapeutics.