Telomerase is a ribonucleoprotein enzyme that uses an internal RNA component as a template for the synthesis of DNA on the ends of chromosomes during cell replication. In mammals, telomerase is normally found only in embryonic cells, germ cells, and, in low levels, in renewal tissue such as leukocytes (Shay et al 1997). Most somatic cells have no telomerase and thus can undergo only a limited number of cell divisions before they senesce. Malignant cells, however, have high levels of telomerase activity, allowing these cells to divide indefinitely. Telomerase has been detected in nearly 90% of tumors of all types tested (Hiyama et all 1995a). All measurements of telomerase activity in tumors reported to date have used cellular material. A less invasive procedure would potentially allow the utilization of telomerase activity as a valuable screening marker and prognostic tool. A plasma assay for telomerase activity could have broad utility as a universal tumor marker.

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