Six of these (CXCL10, CXCL16, CXCL6, FST, PDGFAA, IL‐17B) were functionally screened by siRNA knockdown in prostate cancer cell/fibroblast co‐cultures, revealing a key role for follistatin (FST), a secreted glycoprotein that binds and bioneutralises specific members of the TGF‐β superfamily, including activin A. Expression of FST by both cell types was required for the fibroblasts to enhance prostate cancer cell proliferation and migration, whereas FST knockdown in co‐culture grafts decreased tumour growth in mouse xenografts. Here, IL17B is linked to prostate cancer.