An endobronchial-invading clear cell carcinoma of the thymus: A rare case report

Abstract

Background: Clear cell carcinoma of the thymus (CCCT) is a high-grade and exceptionally rare subtype of thymic carcinoma, accounting for approximately 3% of thymic carcinomas.

Objective: We report a case of CCCT with endobronchial invasion, a rarely documented presentation.

Results: A 50-year-old man presented with progressive dyspnea, hoarseness, hemoptysis, and substantial weight loss over one year. Physical examination revealed tachycardia, tachypnea, and reduced oxygen saturation. Chest radiography demonstrated widening of the superior mediastinum. Contrast-enhanced computed tomography showed a heterogeneous, lobulated mass encasing the superior vena cava and narrowing the bronchial lumen over a 2.5-cm segment above the carina. Bronchoscopy revealed an infiltrative, friable, and easily bleeding mass that nearly obstructed the distal trachea. Histopathologic examination demonstrated a lobulated tumor with dense fibrous stroma, lymphocytic infiltration, and cells with abundant clear cytoplasm, findings consistent with CCCT. The diagnosis was established by integrating the clinical, radiologic, and histopathologic findings. Immunohistochemical analysis and tumor-marker testing were not performed, representing an important diagnostic limitation. The endobronchial invasion extended beyond the typical local invasion pattern described by the International Thymic Malignancy Interest Group, suggesting an unusually aggressive tumor behavior.

Conclusion: This case highlights the diagnostic challenges associated with CCCT. Endobronchial invasion may represent a rare manifestation of this tumor. A complete diagnostic evaluation, including immunohistochemistry and tumor-marker testing, is essential for future cases.