Flow cytometric analysis of circulating endothelial cells and endothelial progenitors for clinical purposes in oncology: A critical evaluation.
Malignant tumors are characterized by uncontrolled cell growth and metastatic spread, with a pivotal importance of the phenomenon of angiogenesis. For this reason, research has focused on the development of agents targeting the vascular component of the tumor microenvironment and regulating the angiogenic switch. As a result, the therapeutic inhibition of angiogenesis has become an important component of anticancer treatment, however, its utility is partly limited by the lack of an established methodology to assess its efficacyin vivo. Circulating endothelial cells (CECs), which are rare in healthy subjects and significantly increased in different tumor types, represent a promising tool for monitoring the tumor clinical outcome and the treatment response. A cell population circulating into the blood also able to form endothelial coloniesin vitroand to promote vasculogenesis is represented by endothelial progenitor cells (EPCs). The number of both of these cell types is extremely low and they cannot be identified using a single marker, therefore, in absence of a definite consensus on their phenotype, require discrimination using combinations of antigens. Multiparameter flow cytometry (FCM) is ideal for rapid processing of high numbers of cells per second and is commonly utilized to quantify CECs and EPCs, however, remains technically challenging since there is as yet no standardized protocol for the identification and enumeration of these rare events. Methodology in studies on CECs and/or EPCs as clinical biomarkers in oncology is heterogeneous and data have been obtained from different studies leading to conflicting conclusions. The present review presented a critical review of the issues that limit the comparability of results of the most significant studies employing FCM for CEC and/or EPC detection in patients with cancer.
Internal Medicine and Medical Oncology, Vigevano Hospital, ASST Pavia, I-27029 Vigevano, Italy.
Marco
M
Danova
Microbiology and Virology, Biotechnology Laboratories, IRCCS San Matteo Foundation, I-27100 Pavia, Italy.
Giuditta
G
Comolli
Medical Oncology, Crema Hospital, Crema I-26013, Italy.
Mariangela
M
Manzoni
Internal Medicine and Medical Oncology, Vigevano Hospital, ASST Pavia, I-27029 Vigevano, Italy.
Martina
M
Torchio
Molecular Genetics Institute, National Research Council and Biology and Biotechnology Department 'L. Spallanzani', University of Pavia, I-27100 Pavia, Italy.
Giuliano
G
Mazzini
biomarkers; circulating endothelial cells; endothelial progenitor cells; flow cytometry; solid tumors