RB1 and osteosarcoma: Necdin strongly suppresses the colony formation of SAOS‐2 osteosarcoma cells, a cell line lacking retinoblastoma protein (Rb) (Taniura et al., 1998) (Figure 10b), indicating that necdin, unlike cyclin‐dependent kinase inhibitors such as p16 and p21, induces mitotic suppression in the absence of Rb.