Polynucleotides encoding rhesus monkey HER2/neu have been isolated, cloned and sequenced. The gene encoding the HER2/neu is commonly associated with the development of epithelial-derived human carcinomas. The present invention provides compositions and methods to elicit or enhance immunity to the protein product expressed by the HER2/neu tumor-associated antigen, wherein aberrant HER2/neu expression is associated with a carcinoma or its development. This invention specifically provides adenoviral vector constructs carrying rhHER2/neu and discloses their use in vaccines and pharmaceutical compositions for preventing and treating cancer.