RB1 and retinoblastoma: While global down-regulation of miRNAs in many tumors have been reported [1], [4], [27], it was also reported that heterozygosity for the Dicer1 allele, but not complete loss of Dicer1 alleles, enhances tumor development in K-ras-driven lung cancer and RB-driven retinoblastoma models [18], [19].