pRB is often described as a component of a regulatory pathway that is inactivated in most cancers (the INK4A/Cyclin D1/pRB/E2F pathway) (Kato et al. 1993; Aagaard et al. 1995; Koh et al. 1995; Lukas et al. 1995; Sherr 1996). Here, RB1 is linked to cancer.