Figure 1.

Heterotypic overview of the cancer secretome. All the microenvironmental, secreted proteins may originate either from cancer cells or from associated stromal cells and their secretion may be triggered by paracrine or autocrine actions between them. Proteomic approaches to capture the tumor microenvironment should focus on identifying proteins secreted by all associated cells, not just the cancer cells. Arrows initiating from cells and pointing in molecules represent secretion; the opposite represents the paracrine or autocrine action of the secreted molecules on the cell types.