Background: Oncoantigens are defined to be proteins that are very specifically expressed in cancer cells and that have the oncogenic activity and high immunogenicity, and are considered to be promising targets for immunotherapy such as therapeutic cancer vaccines. Methods: We have established a strategy as follows to identify new oncoantigens; i) screening of highly transactivated genes in the majority of 120 lung cancers using cDNA microarray representing 27,648 genes coupled with enrichment of tumor cells by laser microdissection, ii) verification of no expression of each candidate gene in normal tissues by northern-blot analysis, iii) validation of the clinicopathological significance of its high level of expression with tissue microarray containing 300 lung cancers, iv) verification of a critical role of each gene in the growth or invasiveness of cancer cells by RNAi and cell growth/invasion assays, v) screening of the epitope peptides recognized by HLA-A*0201- or A*2402-restricted cytotoxic T lymphocyte (CTL). We conducted phase I clinical trials of these therapeutic peptide vaccines for lung cancer patients. Results: We identified 35 oncoantigens and screened dozens of 10-amino-acid peptides, each of which corresponded to a part of TTK, LY6K, IMP-3, CDCA1, KIF20A, CDC45L, and FOXM1, and was a candidate to be presented on the surface of HLA-A*0201 or HLA-A*2402 that induced in vitro CTL response. Phase I clinical studies indicated that five epitope peptides could strongly induce the CTL activity in cancer patients. For example, we conducted a phase I study for HLA-A*2402-positive, advanced non-small cell lung cancer patients who failed to standard therapy, using the combination of 1, 2 or 3 mg/body of each peptides from LY6K, CDCA1, and KIF20A mixed with adjuvant once a week. This cancer vaccine therapy demonstrated tolerability and had very high immunogenicity of even 1 mg/body dose to induce antigen-specific CTLs in cancer patients. Conclusions: Through systematic genomics-based approach and clinical study, we have identified five epitope peptides, which could induce CTLs very effectively in cancer patients, and therefore it warrants further clinical studies. Clinical trial information: NCT01069575.