The protein encoded by the RB1 gene is a negative regulator of the cell cycle and was the first tumor suppressor gene identified. The active, hypophosphorylated form of the protein binds transcription factor E2F1. Inactivation of RB1 and loss of RB1 tumor suppressor function has been identified in approximately 5% of hepatocellular carcinoma and is rare (<1%) in cholangiocarcinoma. RB1 R320* results in early truncation of the RB1 protein and presumably loss of function. The predictive and prognostic significance of RB1 mutations in adenocarcinoma of the liver is undergoing further investigation. It has been suggested that patients with RB1-deficient tumors do not respond to cyclin-dependent kinase (CDK) inhibitors; however, the clinical implication of the loss of a single copy of RB1, as in this patient's case, remains to be fully elucidated. These results should be interpreted in the clinical context.

The protein encoded by the RB1 gene is a negative regulator of the cell cycle and was the first tumor suppressor gene identified. The active, hypophosphorylated form of the protein binds transcription factor E2F1. Inactivation of RB1 and loss of RB1 tumor suppressor function has been identified in many early stage cancers. RB1 alterations are found in approximately 8% of non-small cell lung cancers. RB1 S576fs*34 results in early truncation of the RB1 protein and presumably loss of function. The predictive and prognostic significance of RB1 mutations in lung non-small cell carcinoma is undergoing further investigation. It has been suggested that patients with RB1-deficient tumors do not respond to cyclin-dependent kinase (CDK) inhibitors; however, the clinical implication of the loss of a single copy of RB1, as in this patient's case, remains to be fully elucidated. These results should be interpreted in the clinical context.