This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Oesophagus, Subject name: Surgery
[{'content': 'Most important prognostic factor of cancer esophagus: \nSelect and explain. \nA. Length of growth, B. Depth of involvement, C. Histology grading, D. Immunohistochemistry', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. (b) Depth of invasionRef: Bailey and Love 27th Edition, Page 1085 Prognostic factors of cancer esophagus:* Depth of invasion* Lymph node status* Presence of distant metastasis* Resection margin* Serosal or Peritoneal involvement* Vascular invasion', 'role': 'assistant'}]