RB1 (HGNC:9884) encodes pRB, a commonly mutated tumour suppressor and an important regulator of the cell cycle Even though its best known role is to regulate E2F, databases suggest that pRB interacts with over 300 proteins and may play many other roles such as activating specific genes in response to apoptotic and differentiation signals [33]. This evidence concerns the gene RB1 and neoplasm.