Bhat K, et al. - Researchers investigated whether the use of recombinant human erythropoietin to correct tumor-related or chemotherapy-induced anemia promotes the phenotype conversion of non-tumorigenic breast cancer cells into breast cancer-initiating cells in vitro and in vivo. They also performed a prospective study in a cohort of breast cancer patients who were scheduled to undergo radiation treatment, to assess if elevated endogenous serum erythropoietin levels correlated with increased numbers of tumor-initiating cells. Four established breast cancer cell lines were used. In established breast cancer lines in vitro, an increase in the number of tumor-initiating cells resulting from recombinant erythropoietin was noted. They concluded that the pool of breast cancer-initiating cells was not increased by physiologically slow-rising serum erythropoietin levels in response to tumor-related or chemotherapy-induced anemia, as opposed to large doses of recombinant erythropoietin.