EPO and endometriosis: Other proangiogenic factors, namely, IL-8 [30, 53–56], hepatocyte growth factor (HGF) [57, 58], erythropoietin [59], angiogenin [60], macrophage migration inhibitory factor [61], neutrophil-activating factor [62], and TNF-α [63, 64], are all found at increased concentrations in the peritoneal fluid of patients with endometriosis.