A Pilot Study of Circulating Endothelial and Hematopoietic Progenitor Cells in Children With Sarcomas.

Utilizing a multi-parametric flow cytometry (MPFC) protocol, we assessed various cell-types implicated in tumor angiogenesis that were found circulating in the peripheral blood of children with sarcomas (cases) based on their cell surface antigen expression. Circulating endothelial cells (CECs), endothelial colony forming cells (ECFCs) and the ratio of two distinct populations of circulating hematopoietic stem and progenitor cells (CHSPCs), the pro-angiogenic CHSPCs (pCHSPCs) and non-angiogenic CHSPCs (nCHSPCs) were enumerated. MPFC was analyzed in cases at baseline and at 4 additional time-points until the end of treatment and levels compared with each other and with healthy controls. At all time-points, cases had significantly lower levels of CECs, but elevated ECFCs and a pCHSPC:nCHSPC ratio compared to controls (all p values <0.05). There was no significant difference in any of the cell types analyzed based on tumor-histology, stage (localized v/s metastatic) or tumor-size. After treatment, only the CECs among the complete responders were significantly lower at end of therapy (p<0.01) compared to non-responders, whereas the ECFCs among all cases significantly increased (p<0.05)) compared to baseline. No decline in the pCHSPC:nCHSPC ratio was observed despite tumor response. Based on these results, a validation of CECs as prognostic biomarker is now warranted.