This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
[{'content': 'A child is born with a single functional copy of a tumor suppressor gene. At the age of 5 years, the remaining normal allele is lost through mutation. As a result, the ability to control the transition from G1 to the S phase of the cell cycle is lost. Which of the following neoplasms is most likely to arise by means of this mechanism - \nSelect and explain. \nA. Retinoblastoma, B. Breast carcinoma, C. Adenocarcinoma of colon, D. Cerebral astrocytoma', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]