RB1 and oligodendroglioma: On the other hand, Watanabe et al, (2001) identified this anomaly in three of 48 tumours, suggesting that promoter alteration of RB1 is rare in oligodendrogliomas, and demonstrated that inactivation of the RB1-mediated G1->S cell-cycle transition pathway is more frequently caused by CDK4 amplification or p16INK4A/p15INK4B inactivation.