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
Second primary tumor of Head and Neck is most commonly seen in malignancy of - 
Select and explain. 
A. Oral cavity, B. Larynx, C. Hypopharynx, D. Paranasal sinuses
A: Oral cavity
Answer: A: Oral cavity 
Explanation: "The site of the index cancer influences the most likely site of a second primary malignancy. As an example, in a series of 1257 patients with squamous cell carcinoma of the head and neck, patients with an index malignancy arising in the larynx were more likely to develop a second primary cancer in the lung, while those arising in the oral cavity were more likely to develop a second primary in the head and neck or esophagus. This relationship has been observed in other studies as well."