In the present study, we explored if erythropoietin increases the plasticity of breast cancer cells and tested the hypothesis that elevated endogenous serum erythropoietin levels in breast cancer patients increase the aggressiveness of breast cancer through expansion of the pool of BCICs, analogous to the effects seen after treatment of breast cancer cell lines with rhEpo and the unfavorable results from randomized trials using rhEpo in anemic cancer patients [12, 44, 45]. The gene discussed is EPO; the disease is breast cancer.