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: ENT
A chronic smoker, age 55 yrs presented with complaints of hemoptysis. On bronchoscopic examination there was a lesion in the distal trachea growing into the lumen. Most probable diagnosis is: 
Select and explain. 
A. Squamous cell Ca, B. Adenoid cystic Ca, C. Mucoepidermoid Ca, D. Squamous papilloma
A: Squamous cell Ca
Answer: A: Squamous cell Ca 
Explanation: Squamous cell carcinoma is the cancer most frequently found in men and is highly correlated with cigarette smoking. Histologically, cells develop a pattern of clusters with intracellular bridges and keratin pearls. Impoantly, squamous cell carcinoma is primarily located centrally and arises in the major bronchi, often causing the typical symptoms of centrally located tumors, such as hemoptysis, bronchial obstruction with atelectasis, dyspnea, and pneumonia.