KRAS and central nervous system cancer: We compared the extent of MC infiltration in tumors, induced with a combination of two oncogenes (KRas+Akt) in two different transgenic lines (Ntv-a and Gtv-a), each carrying a deficiency in either of the tumor suppressors Ink4a or Arf. We found that the number of MCs in high-grade tumors generated in Arf-deficient mice was significantly higher than in low-grade gliomas formed in Ink4a-deficient mice, thus suggesting that accumulation of MCs accompanies development of high-grade gliomas.