RB1 and retinoblastoma: Several reports suggest that the development of retinoblastoma in individuals with RB1 loss may also be driven by additional factors such as epigenetic alterations (including histone H3K4 methylation and H3K9/H3K14 acetylation), copy number variations (in genes such as Kif14, Mdm4, E2f3, Dek, and Cdh11), or inactivating mutations in the BCL-6 co-repressor [18,19].