Abstract
BACKGROUND: Thymoma, the most common tumor of the anterior mediastinum, originates from the epithelial cells of the thymus. The World Health Organization (WHO) classifies thymomas into several subtypes based on histopathological features: type A, AB, B1, B2, and B3. Type A thymomas are generally considered low-risk due to their indolent behavior; hence, distant metastasis, particularly to the lungs, is exceptionally rare. Managing such advanced cases requires individualized treatment approaches. CASE DESCRIPTION: A 50-year-old male presented with right shoulder pain persisting for over a month. A chest computed tomography revealed a 43 mm × 40 mm anterior mediastinal mass with multiple small nodules scattered in both lungs. Positron emission tomography-computed tomography confirmed a hypermetabolic mediastinal mass and non-metabolic lung nodules, suggestive of thymoma with pulmonary metastasis, clinically staged as T1N0M1a (IVA). Due to the small size of the primary tumor and lack of invasion, surgery was chosen to alleviate symptoms, establish a definitive diagnosis, reduce tumor burden, and guide treatment. Subsequently, the patient underwent thoracoscopic resection of the primary tumor and biopsy of the left lower lung nodule. Histopathology confirmed type A thymoma, characterized by sheets of oval or spindle-shaped cells with abundant cytoplasm. Immunohistochemical staining showed positivity for cytokeratin (CK) (AE1/AE3), CK5/6, p63, and CD99, and negativity for epithelial membrane antigen (EMA), terminal deoxynucleotidyl transferase (TDT), CD20, CD117, and Vimentin, with a Ki-67 index of approximately 5%. The lung nodule exhibited similar immunohistochemical profiles but had a higher Ki-67 index (8%), indicating increased proliferative activity. Postoperatively, the patient received four cycles of systemic chemotherapy {[cyclophosphamide, adriamycin (doxorubicin), and cisplatin] (CAP) regimen: cyclophosphamide, doxorubicin, and cisplatin}. Over 5 years of follow-up, there was no recurrence of the primary tumor, and the metastatic lesions remained stable. CONCLUSIONS: This case demonstrates the potential benefits of combining surgery and systemic chemotherapy in managing advanced thymoma with metastasis. The patient’s 5-year survival and stable disease status highlight the importance of individualized treatment strategies and continuous monitoring to achieve favorable outcomes.