Primary tumors create a favorable microenvironment, namely, pre-metastatic niche, in secondary organs and tissue sites for subsequent metastases. The pre-metastatic niche can be primed and established through a complex interplay among primary tumor-derived factors, tumor-mobilized bone marrow-derived cells, and local stromal components. We review here our current understanding of the key components and underlying mechanisms for pre-metastatic niche formation. We propose six characteristics that define the pre-metastatic niche, which enable tumor cell colonization and promote metastasis, including immunosuppression, inflammation, angiogenesis/vascular permeability, lymphangiogenesis, organotropism, and reprogramming. We highlight the significance of the pre-metastatic niche, and discuss potential implications and future research directions.
Keywords: cancer intervention; immunosuppression; inflammation; metastasis; pre-metastatic niche; tumor-host interaction.
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