Tumorogenesis in aging is due to

Telomerase, also called terminal transferase, is a ribonucleoprotein that adds a species-dependent telomere repeat sequence to the 3' end of telomeres. A telomere is a region of repetitive sequences at each end of a eukaryotic chromosomes in most eukaryotes. Telomeres protect the end of the chromosome from DNA damage or from fusion with neighbouring chromosomes. The fruit fly Drosophila melanogaster lacks telomerase, but instead uses retrotransposons to maintain telomeres. Telomerase is a reverse transcriptase enzyme that carries its own RNA molecule (e.g., with the sequence "CCCAAUCCC" in veebrates) which is used as a template when it elongates telomeres. Telomerase, active in normal stem cells and most cancer cells, is normally absent from, or at very low levels in, most somatic Cells.