Role of bone marrow-derived cells in colon cancer: lessons from mouse model studies

The role of the tumor stroma in carcinogenesis and cancer progression have been documented for a long time. However, the molecules and mechanisms involved have not been understood precisely. Recently, various mediators involved in the communication between the tumor epithelium and stroma and their roles have been revealed by utilizing new technology such as array analysis, laser capture sampling, and genetically altered mice. Moreover, accumulating evidence indicates that some cells in the tumor stroma are derived from the bone marrow (BM). While some of these BM-derived cells are well-known players in inflammation, as exemplified by macrophages, other types of BM-derived cells have been described only recently and are still poorly characterized. In this review, I focus on the latter class of BM-derived cells in colon carcinogenesis, with reference to similar cells in other types of cancer as well. Studies of these myeloid cells should help us understand the inflammation and immune response from a broader perspective as the body's reaction to pathogenic insults.