PRPS2 and histiocytic sarcoma: Further, mice from the BAC #1 lines developed earlier and more florid histiocytic proliferation more typical in appearance and showing the classic organ predilection (reproductive, hematopoietic, hepatic) of histiocytic sarcoma [44], [47], which may be related to the PRPS2 gene driving aggressive disease at an earlier age or to the site or copy number of BAC integration.