It was reported that AP-1 (FOS and JUN) transcription factor is critical for the growth and proliferation of breast cancer cells47 and is also involved in the stimulation of NF-κβ transactivation activity.48 In erythroid cells, Epo was reported to co- or posttranslationally increase AP-1 activity.49 We therefore performed rHuEpo treatment of MCF-7 and MDA-MB-231 cells in order to assess the effect of rHuEpo treatment on cell proliferation and its potential to synergize with cDDP in suppression of breast cancer cell growth. The gene discussed is FOS; the disease is breast cancer.