Expression pattern of many testis specific genes has been analyzed in different tumors since then and many of them have been shown to be expressed in various histological tumor types. The probable role of CT (Cancer-Testis Antigens) genes as stem cell marker as well as cancer biomarker has been proposed for a long time, but the evidences supporting their role as CSC marker are few. This is partly because CSC (cancer stem cells) hypothesis has just recently gained attention. Pattern of CT antigens expression should be compared in normal stem cells vs. CSCs. If they are shown to be expressed widely in normal tissue stem cells, possible side effects might put their application in immunotherapeutic approaches under question.