Based on the results of present study and published reports showing the presence of pluripotent markers (OCT-4, NANOG and SOX2) in human myometrial side population and expression of particularly OCT-4A in human leiomyomas, we speculate that these nuclear OCT-4 positive stem cells located in the perimetrium are the possible tumor initiating cells leading to the development of leiomyomas rather than the mesenchymal cells which express cytoplasmic OCT-4B. This evidence concerns the gene NANOG and neoplasm.