The Kit D818Y (#26, #57, #92, #223) or Nras Q61H (#28, #39) mutations, identified in 45 and 20% of mice, respectively, have been previously shown to confer growth factor independency in the TgSpi1FA+/+ cells or myeloma cells, respectively [15, 40], indicating a causal relationship between constitutively activated KIT and RAS pathways and growth factor independence. Here, KIT is linked to plasma cell myeloma.