Background: Life-threatening metastases developing in organs distant from a malignant tumor must derive from cells that have been disseminated from the primary tumor and are capable of resettling and growing. Therefore, the question arises how and whether such cells which have the potential to grow into metastases can be detected in peripheral blood.

Materials and Methods: Using a nondissipative approach with only one enrichment step of red blood cell lysis, all white cells from 1ml of peripheral blood from patients with breast, colon, lung and pancreatic cancers were cultured under conditions favoring the growth of epithelial cells. At 7, 14 and 21days the cell cultures were inspected for the appearance of spheroids staining with anti-EpCAM, anti-CD24 and anti-CD44 antibody and expressing ALDH1. Subsequently spheroids were spun down, isolated into single cell suspensions and re-cultured.

Results: Tumorspheres from peripherally circulating cells from patients with malignant tumors in different stages of disease could so far be grown from 79% of patients in whom more than 1000 epithelial tumor suspect cells per ml were detected. The size of the spheres increased from day 7 to day 21. They were negative for CD24 and positive for CD44 and highly express ALDH1 and thus exhibite typical features of stem cells. Numbers of tumorspheres correlated with the aggressiveness of the tumor. Re-culturing of single cell suspensions resulted in regrowth of tumor spheres indicative of self-renewal potential of these cells.

Conclusion: Here, we demonstrate that the circulating tumor cells, detected in our approach contain a subpopulation of cells capable of growing into tumorspheres. with stem cell-like properties and self-renewal capacitiy.

The frequency of these cells capable of forming tumorspheres in peripheral blood seems to be dependent on the aggressiveness of the primary tumor.