The initial step of premetastatic niche formation in specific organ sites is mediated by tumor‐derived soluble factors such as TNF‐α, TGF‐β, CXCL12, placental growth factor and VEGF‐A49 as well as by tumor‐derived exosomes.50, 51, 52. The gene discussed is CXCL12; the disease is neoplasm.