True about telomerase:

After each mitosis (cell doubling), there is progressive shortening of telomeres which are the terminal tips of chromosomes. Telomerase is the RNA enzyme that helps in repair of such damage to DNA and maintains normal telomere length in successive cell divisions. However, it has been seen that after repetitive mitosis for a maximum of 60 to 70 times, telomeres are lost in normal cells and the cells cease to undergo mitosis. Telomerase is active in normal stem cells, but not in normal somatic cells. Cancer cells in most malignancies have markedly upregulated telomerase enzyme, and hence telomere length is maintained. Thus, cancer cells avoid ageing, mitosis does not slow down or cease, thereby immortalising the cancer cells. Mohan H. Textbook of pathology. Jaypee Brothers Medical Publishers; 2015. Edition 7. Page 208