Telomeres, telomerase, and cancer: life on the edge of genomic stability

The presence of telomerase activity in most human tumors, but not in many normal somatic tissues, has raised considerable interest in telomerase as a possible anticancer therapy. Recent advances in the cloning and characterization of mammalian telomerase components have paved the way for a more detailed understanding of the role of telomerase and telomere length maintenance in cell proliferation. Here, we summarize the most recent biochemical and genetic evidence suggesting that telomere length maintenance by telomerase is critical to the proliferative ability of some immortalized mammalian cells in culture and in vivo.