Abstract: An isolated antigenic peptide fragment that is an isolated oncogene protein fragment is disclosed. The isolated peptide fragment of the invention is a peptide either 9 or 10 amino acid residues in length that includes at least a leucine residue at the C- terminus (i.e., position 9 or position 10). The peptide fragment is capable of binding in an HLA-A2 binding cleft and is capable of stimulating proliferation of at least one tumor-specific cytotoxic T-lymphocyte. Preferred peptides further include an isoleucine residue at position 2 and a valine residue at position 6. The most preferred isolated peptides can stimulate proliferation of cytotoxic T-lymphocytes obtainable from peripheral blood lymphocytes, ovarian tumors, breast tumors, gastric tumors, non-small cell lung tumors, pancreatic tumors, colon tumors, gliomas, bladder tumors, endometrial tumors and neuroblastomas. The preferred isolated peptide of the invention is a mutant peptide defined by SEQ ID NO.:2 or its functional equivalents.