Colorectal cancer (CRC) is a frequently lethal disease with heterogenous clinical outcomes and responses to therapy. The tumor microenvironment is populated with immune cells, where the heterogeneity in immunological composition, spatial distribution and function has a large impact on clinical outcomes and therapeutic responses. The interplay between immune components and cancer cells in the tumor microenvironment could be a key to improve anti-tumor immune responses in CRC. Among infiltrating immune cells, mast cells are one of the first immune cells recruited to tumor sites and exhibit an extraordinary ability to respond rapidly by releasing granule-stored and newly made mediators, which underpins their importance in cancer progression. Mounting evidence has shown the correlation of mast cell number and CRC progression in human. However, the role of mast cells in CRC is also considered contradictory and the mechanism how they influence cancer growth still remains obscure. Therefore, this thesis aimed to investigate the impact of mast cells on colon cancer growth and delineate the molecular mechanism of how these cells interact with each other by using human mast cells in in vitro 2D and 3D coculture with colon cancer cells.