CDKN2A and brain neoplasm: In the background of heterozygous INK4A/Arf deletion (Nestin-Cre; PdgfraK/+; INK4A/Arf+/−), animals developed brain tumors only rarely, and cohort mice with heterozygous INK4A/Arf mutation alone (INK4A/Arf+/−) never developed brain tumors (Fig. S3a).