Mast cells (MCs) are mediators of allergy and inflammation and participate in the growth of cancer cells. MCs can promote both neoangiogenesis and tumor growth. They increase in the stroma of certain tumors where they can be recruited by tumor-derived chemoattractants, such as monocyte chemotactic protein-1 (MCP-1), RANTES and stem cell factor (SCF) to selectively secrete inflammatory molecules including chemical mediators and cytokines (TNF, IL-6 and IL-1). However, MC differentiation pathways and heterogeneity in cancer are still poorly understood. Human interleukin 1 (IL-1) plays a pivotal role in the pathogenesis of many diseases and functions, including host response to microbial invasion, injury inflammatory processes, immunologic challenges and cancer. Inflammation around the tumor includes the infiltration of mast cells and facilitates cancer growth. MCs are activated by IL-1 which can be produced by certain cancer cells and stimulate the stromal cells to selectively release IL-6, contributing to the development of Th-17 cells and increasing inflammation. IL-37, mainly generated by macrophage cell line, is an IL-1 family member which binds IL-18 receptor α (IL-18Rα) chain, and acts as a natural inhibitor of immune responses. IL-37 down-regulates cJun induced by IL-1, pro-inflammatory signals and reduces the expression of the mitogen-activated protein kinase (MAPK) p38α, STAT transcription factors and p53, affecting cellular differentiation and proliferation. In the present study we report the relationship between inflammatory mast cells, cancer and the beneficial effect of IL-37.