1. Based on the data in current study, we suggest a model for the macrophage enhancement of metastasis at the distal target organ. Following arrest of the tumor cells in capillaries of metastasis target organ, monocytes are quickly recruited and differentiate in situ into metastasis associated macrophage phenotype whereafter they promote the extravasation, survival and persistent growth of metastatic tumor cells. Qian BZ et al, PLoS One 2009 Endothelial cell Disseminated tumor cell Seeding Persistent Growth Initial Growth Monocytes Metastasis recruited macrophages New blood vessel Metastasis tumor cell Proteases Survival/Growth Factors Angiogenic factors Extravasation