Figure 1. The role of the ELR⁺CXCL chemokine family member CXCL7 in autocrine and paracrine activation loops between cells in the tumor microenvironment. Cross-talk exists between malignant cells and normal cells of the microenvironment through the intermediary of the ELR⁺CXCL chemokine family, particularly CXCL7 and their (C-X-C) receptors, CXCR1 and CXCR2. CXCL7, potentially up-regulated by IL-1β secreted by inflammatory cells, activates signaling cascades (e.g., ERK/PI3K) stimulates cancer and endothelial cell proliferation and participates in the attraction of neutrophils and macrophages. These mechanisms are dependent upon the expression of CXCR1 and CXCR2, physiologically expressed by normal cells of the tumor microenvironment but aberrantly expressed by neoplastic cells. Hence, the CXCL7 and CXCR1/CXCR2 signaling axis is crucial for tumor growth and angiogenesis, as well as for the maintenance of the tumor inflammatory context.