hTERT expression and telomere length in normal somatic cells and precancerous cells. hTERT expression and telomere length in normal somatic cells and precancerous cells. Human telomerase reverse transcriptase (hTERT) activity is overexpressed in the majority of cancers. hTERT plays a pivotal role in the evasion of cellular senescence and subsequent immortalization of precancerous cells. In normal somatic cells, hTERT is only expressed at a basal level and telomeric ends are continually degraded with each cycle of cellular replication, eventually leading to senescence. However, in precancerous cells, telomeres are maintained via increased hTERT expression and cells are able to avoid mechanisms that would prevent immortalization. Michael Daniel, and Trygve O. Tollefsbol J Exp Biol 2015;218:59-70 © 2015. Published by The Company of Biologists Ltd