VEGFR2 expressing circulating (progenitor) cell populations in volunteers and cancer patients

Circulating cells of several lineages are thought to participate in angiogenesis and tumor growth. Experimental studies in tumorbearing mice have pointed to the potential importance of VEGFresponding circulating (endothelial) progenitor cells in tumor growth.We have studied circulating CD31- and/or CD34-positive cell populations with a low to moderateVEGFR2 expression in human volunteers and cancer patients. We recognized four cell populations, which were further characterized by their content of major hematopoetic progenitor, monocytic, endothelial and platelet markers. After establishing the test-retest stability of the measurements in nine patients, we determined the frequencies of the various cell populations in a group of 20 volunteers and 14 cancer patients.Two populations were markedly increased in cancer patients. Small CD45neg /CD34bright/VEGFR2+ cells amounted to 12 and 64 cells/ml (P