Myeloid cell trafficking and tumor angiogenesis.

Tumor growth and metastasis depend on neovascularization, the growth of new blood vessels. Recent findings have revealed that tumor neovascularization is regulated in part by monocytes, which are myeloid lineage cells from the bone marrow. Tumors exhibit significant monocyte infiltrates, which are actively recruited to the tumor microenvironment. Upon tumor infiltration, monocytes can participate in tumor neovascularization. Monocytes can either differentiate into macrophages, which express proangiogenic growth factors, or into endothelial-like cells, which may directly participate in neovascularization. Preliminary studies in animals suggest that modulation of bone marrow-derived cell trafficking into tumors will provide a useful new approach in cancer therapy.