​Cancer cells characteristically express high levels of telomerase.

Telomerase is an enzyme that adds short repeated sequences of DNA to the ends of chromosomes, called telomeres, which protects them from degradation and ensures the stability of the genetic material. Normal somatic cells have limited telomerase activity, meaning that their telomeres gradually shorten with each cell division and eventually trigger a process of cell senescence or apoptosis. However, many cancer cells have acquired mutations that re-activate telomerase expression, allowing them to maintain their telomeres and undergo unlimited proliferation. Therefore, telomerase is a key marker and target for cancer diagnosis and therapy.