Unlimited Mileage from Telomerase?

Last year, scientists from the company Geron reported that inserting the gene for telomerase--the enzyme that makes the protective ends of chromosomes and is turned on in many tumors--into fibroblasts can prolong their ability to replicate, up to 100 generations. But how is this different from what happens in cancer cells? In their Perspective, de Lange and DePinho explore new evidence that begins to sort out the controls of cellular replication and oncogenesis. They liken the function of telomerase to that of a gas tank in a car, with oncogenes as the gas pedal and tumor suppressors as the brake.