MDSC expansion is associated with faster tumor growth in Irf8-/- mice than in WT B6 mice, while expansion of MDSC is diminished during tumor growth in transgenic mice that over-express Irf8. The expression of Irf8 is down-regulated in breast cancer patients, and the level correlates inversely with the frequency of peripheral MDSC. This evidence concerns the gene IRF8 and neoplasm.