Many G-CSF-producing tumors are suggested to be biologically highly malignant, poorly differentiated, and highly invasive to local lesions and vessels for the following reasons: (1) autocrine tumor growth because of the emergence of G-CSF receptors on tumor cells, (2) promotion of tumor growth and spread by proliferating neutrophils because of G-CSF, and (3) the inhibition of cellular immunity mediated by macrophages or natural killer cells by G-CSF. The gene discussed is CSF3R; the disease is neoplasm.