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: Surgery
[{'content': 'M.C. site of CA oesophagus is - \nSelect and explain. \nA. Middle 1/3rd, B. Upper 1/3rd, C. Lower 1/3rd, D. Lower end of esophagus', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Esophageal Carcinoma is of two common histological types\n\n\nSquamous cell Ca - the MC type in the world (-95% according to Sabiston)\nAdenocarcinoma - where incidence is increasing at a rapid rate and is now the MC type in the USA (Ref:• Harrison, Schwartz)\n\n\nDistribution of Squamous Cell Ca.\n\nUpper 1/3\xa0→\xa010%\nMiddle 1/3 →\xa060%\nLower 1/3\xa0→\xa030% \xa0 \xa0\xa0\n\nAdenocarcinoma is mainly located in lower 1/3.\nNowhere, I could get the MC site of esophageal carcinoma overall (including both squamous and adeno variety). \nBut one thing is sure - squamous cell Ca is the MC type of esophageal cancer in the world \n\n\nSo I presume that the overall MC site would be the MC site involved by the MC type of esophageal cancer i.e. → Middle 1/3\n\nSo remember\nMC type of esophageal Ca in world → Squamous Cell Ca (-95%) MC site → Middle 1/3', 'role': 'assistant'}]