Telomeres are protective caps on chromosomes. They are maintained by telomerase.
Gene therapy with telomerase does not increase the risk of cancer - health science news

Regeneration of damaged tissue may benefit greatly from the activity of telomerase, but scientists have been hesitant to exploit this further because higher telomerase activity might increase the risk of cancer. Telomerase is an enzyme that builds telomers at the end of chromosomes to protect them from damage, and keeps cells dividing. In adult cells, telomerase is no longer active, except in cancer cells. In a new study in lung cancer-prone mice, scientists have shown that delivery of telomerase by viral means does not lead to cancer development, not even in this “worst case scenario”, and thus appears to be safe. Telomerase might therefore become a treatment option for tissue repair and rejuvenation in the future.

Read the full story: Spanish National Cancer Research Centre (CNIO)
Scientific publication: PLoS Genetics