Neutrophils, the most abundant leukocyte in human circulation are being more and more recognized as part of the immune reaction to cancer. In the last years, the understanding that neutrophils possess a dual role in cancer development has emerged. During tumor progression the number of neutrophils increase, and their phenotype change. In advanced cancer, we can find several sub-populations of circulating neutrophils possessing different characteristics of maturity, tumor cytotoxicity and immune suppression. One important sub-population of circulating neutrophils is the granulocytic myeloid derived suppressor cells (G-MDSC). Differencing G-MDSC from other sub-populations of neutrophils in the circulation is a complex and controversial task, as there are no clear definitions of the differences between these granulocytic sub-populations. Herein we review the differences described thus far between G-MDSC and other circulating neutrophils. We then compare the morphology, surface markers, function and prognostic importance of the different tumor-related circulating neutrophils, as described by us and others, and discuss the possible relations between the different sub-populations, their source and fate. Lastly, we suggest a nomenclature to try and encompass the full range of circulating neutrophils in cancer.
Keywords: Cancer; Neutrophils; Tumor immunology.
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