What is the most common mediastinal tumor?

• A. Small Cell Lung CA
• B. Thymoma
• C. Carcinoid tumor
• D. Adenocarcinoma Lung CA

Answer: (B)

Thymoma arises from thymic tissue in the anterior mediastinum and is the most common primary tumor of the mediastinum in adults. The mediastinum is the central chest compartment, and the thymus sits in the anterior part of it, so tumors that originate there—thymomas—are by far the most frequent mediastinal tumors. In contrast, the listed lung cancers originate in the lung itself (often the central airways or peripheral lung tissue) rather than the mediastinal thymic tissue, and carcinoid tumors, while they can occur in the mediastinum, are much less common than thymomas. Thus thymoma is the best answer.