TERT and embryonal carcinoma: Epigenetic mechanisms may be responsible for reversible silencing of the TERT during differentiation and stem cell research has the potential to contribute to our knowledge of down-regulation of TERT and other related gene regulations [69,121] Retinoic acid treatment of human embryonal carcinoma and human promyelocytic leukemia cell lines resulted in a decline in telomerase activity during differentiation [122].