Based on these findings, it is tempting to speculate that differences in the capacity for or consequences of recognition of tumor cell-expressed CD47 by SIRP-α-expressing macrophages in NOD.SCID versus C57BL/6 mice may contribute to the ability of intra-muscularly injected p16p19−/−; Kras(G12V) tumor cells to generate histiocytic sarcomas in NOD.SCID but not C57BL/6 recipients, as reported here. This evidence concerns the gene KRAS and histiocytic sarcoma.