RB1 and neoplasm: RB1 encodes the retinoblastoma protein, a tumor suppressor and negative regulator of the cell cycle (Figure 2).[18] The loss of RB1 protein expression has been linked to poor survival and may prognosticate a decreased response to kinase inhibitors.[18] RB1 mutations have been reported sporadically in HCC.[7] At the time of referral to the CCTT the patient had metastatic disease to the right pterygoid fossa and liver and his clinical condition precluded experimental therapy.