Detection of circulating carcinoma cells by telomerase activity

Telomerase has been shown to be a marker of epithelial cancer cells. We developed a method that allows the detection of circulating carcinoma cells in the blood of cancer patients. Circulating epithelial cells are harvested from peripheral blood mononuclear cells by immunomagnetic separation using BerEP4-coated beads. A telomeric repeat amplification protocol (TRAP)-ELISA is then used to measure telomerase in harvested epithelial cells. This method is specific and sensitive as demonstrated by experiments using BerEP4-positive and negative cell lines. Whereas we never found telomerase activity in harvested epithelial cells (HEC) samples from 30/30 healthy donors, we have detected telomerase activity in HEC from 11/15 (73%) patients with stage IIIB or IV non-small cell lung cancer (NSCLC) patients and from 8/11 (72%) stage C or D (Dukes classification) colon cancer patients. This non-invasive method could be of great value as a diagnostic or prognostic marker, or for monitoring cancer progression.