Further investigation led to the discovery that granulocyte-macrophage colony-stimulating factor (GM-CSF) with a molecular weight of ~14 kDa was abundant in 4T1-CM.45 Its level in the serum and lungs of 4T1 tumor-bearing mice on day 14 was notably increased (Fig. 4a, b and Supplementary Fig. S6b). The gene discussed is CSF2; the disease is neoplasm.