Erythropoietin and erythropoietin receptor expression in human cancer

Erythropoietin (EPO) stimulates the growth of erythroblasts in the bone mar row (C, Lacombe and P. Mayeux, Nephrol, Dial. Transplant., 14 (Suppl, 2): 2 2-28, 1999), We report basal and hypoxia-stimulated expression of EPO and i ts receptor, EPOR, in human breast cancer cells, and we demonstrate EPO-sti mulated tyrosine phosphorylation and the proliferation of these tells in vi tro. In 50 clinical specimens of breast carcinoma, we report high levels of EPO and EPOR associated with malignant cells and tumor vasculature but not with normal breast, benign papilloma, or fibrocystic tissue. Hypoxic tumor regions display the highest levels of EPO and EPOR expression. Enhanced EP O signaling may contribute to the promotion of human cancer by tissue hypox ia.