TTK and esophageal cancer: In this regard, TTK, LY6K, and IMP3 molecules used in the present trials are considered to be most appropriate because they were expressed in the great majority (> 95%) of esophageal cancers, were expressed specifically in cancer cells and testis (cancer-testis antigens), were shown to be essential for survival of cancer cells, and most importantly revealed very strong immunogenicity [6-12].