Growth of tumorspheres from peripherally circulating tumor cells.

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2 Background: Even after the complete resection of a malignant tumor the menace remains, that cells that have dissociated from the tumor might resettle in distant organs and grow into life-threatening metastases. Therefore we have developed an approach (maintrac) to detect and monitor the circulating tumor suspect epithelial cells in blood. However, the question arises whether these cells have the potential to grow into metastases. Methods: Using a nondissipative approach with only one enrichment step of red blood cell lysis, the cells from the pellet, containing the white blood cells together with the putative tumor cells were cultured under conditions favoring the growth of epithelial cells. At 7, 14, and 21 days the cultured cells were stained with anti-EpCAM antibody and inspected for the appearance of epithelial antigen positive spheroids. Results: Peripherally circulating cells from patients with malignant tumors in different stages of disease were analyzed for the presence of circulating epithelial tumor suspect cells and the frequencies of tumorspheres. Tumorspheres could so far be grown from all of 20 patients in whom more than 2000/ml epithelial tumor suspect cells were detected. Fractions of tumorspheres varied from less than 1% of the epithelial tumor suspect cells in patients with primary breast cancer to up to 70% in a patient with an aggressively growing metastatic colon cancer. The size of the spheres increased from day 7 to day 21 but already had reached the size of day 21 colonies after seven days in the patient with the metastatic colon cancer. Conclusions: Here, we demonstrate that the tumor suspect cells, detected in our approach contain a subpopulation with stem cell-like properties capable of growing into tumorspheres. The frequency and growth potential of cells capable of forming spheres seems to be dependent from the properties of the primary tumor. The possibility to grow tumorspheres from peripherally circulating tumor cells may open up a new field, where the relevant cells with stem cell properties from individual patients can now be specifically analysed further for genetic endowment, transcriptional activity, heterogeneity, and stem cell markers.