In contrast, in the heritable form, a germline RB1 mutation (M1) is present in all body cells with somatic (M2) mutations in multiple retinal cells, increasing the risk of bilateral (80%) and multifocal (67%) retinoblastomas with an early age of onset and secondary non-ocular cancers later in life [6,11,27]. The gene discussed is RB1; the disease is retinoblastoma.