Telomerase in human tumors: molecular diagnosis and clinical significance

Shortening of structures known as telomeres, which cap the ends of chromosomes, is postulated to limit the lifespan of human cells. Activation of telomerase, an enzyme that synthesizes telomeric DNA, is an essential step in cell immortalization. Telomerase is ordinarily inactive in most somatic cells, but can be detected in nearly all tumors. The activation of telomerase in malignant cancers seems to be an important step in tumorigenesis, whereby the cell gains the ability of indefinite proliferation. Due to the association between telomerase expression and malignancy, the enzyme is expected to be a useful tumor marker and a new anticancer therapeutic target. However, recent results scale down to some extent the initial enthusiastic expectations for telomerase as the ideal malignancy marker.