Unlike in naïve SHIP−/− mice or SHIP−/− mice with 67NR tumors (Fig. 2D–2F), 4T1 tumor-bearing SHIP−/− mice possessed MDSCs that expressed Arg1 (Fig. 4A) and were over 40-fold more immunosuppressive on a per cell basis than MDSCs isolated from 4T1 tumor-bearing WT mice (Fig. 4C). This evidence concerns the gene ARG1 and neoplasm.