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Figure 1. Multiple roles of A_2B adenosine receptors in cancer. A_2B receptor stimulation induces (1) the differentiation of human monocytes, mouse peritoneal macrophages (φ) and hematopoietic progenitor cells (HPCs) into tolerogenic dendritic cells (DCs); (2) the expansion and accumulation of MDSCs; (3) Treg differentiation, enhancing immune suppression that inhibits T-cell responses. Activation of A_2B receptors on stroma cells, including tumor cells, endothelial cells and fibroblasts promotes tumor proliferation or invasion and angiogenesis. TNBC: triple negative breast cancer; VEGF: vascular endothelial growth factor; IL-8: interleukin-8; bFGF: basic fibroblast growth factor; CXCL12: C-X-C motif chemokine ligand 12; MDSCs: myeloid-derived suppressor cells