For cancer cells to develop, they must overcome the finite proliferative capacity associated with normal cells. Many recent studies have identified that telomeres, the protective structures found at the end of eukaryotic chromosomes, are important in this process. Telomere length is maintained by a ribonucleoprotein enzyme known as telomerase. Unlike normal cells where telomerase expression is repressed, this enzyme is found in approximately 80% of human cancers. The expression and activity of telomerase is essential for the infinite growth associated with tumour cells.