Metastasis is a very complicated multi-step process and accounts for the low survival rate of the cancerous patients.To metastasize,t he malignant cells must detach from the primary tumor and migrate to secondary sites in the body through either blood or lymph circulation.Macrophages appear to be directly involved in tumor progression and metastasis.However,the role of macrophages in affecting cancer metast asis has not been fully elucidated.Here,we have utilized an emerging technique,namely in vivo flow cytometry(IVFC)to study the depletion kinetics of circulating prostate cancer cells in mice and determine how depletion of macrophages by the liposome encapsulated clodronate affects the depletion kinetics.Our results show diferent depletion kinetics of PC-3 cells between the macrophagedeficient group and the control group.The number of circulating tumor cells(CTCs)in the macrophage-deficient group decreases in a slower manner compared to the control mice group.The differences in depletion kinetics indicate that the absence of macrophages facilitates the stay of prostate cancer cells in circulation.In addition,our imaging data suggest that macrophages might be able to arrest,phagocytose and digest PC-3 cells.Therefore,phagocy tosis may mainly contribute to the de-pletion kinetic diferences.The developed methods elaborated here would be useful to study the relationship between macr ophages and tumor metastasis in small animal cancer models.
