Since BMP4 has been shown to promote the development of stress erythroid progenitors in spleen [15, 18] and we witnessed an erythropoietic response in the spleen of tumor-bearing mice, we assessed BMP4 expression in the spleen of 4T1 breast tumor model; we found that BMP4 in the spleen was increased at the mRNA and protein level under tumor-stress conditions (Fig 4BC). The gene discussed is BMP4; the disease is neoplasm.