Mediastinal Seminoma with an Elevated Level of Serum Angiotensin-converting Enzyme

A 22-year-old man was admitted following the detection of right hilar enlargement during a medical checkup. The patient's serum angiotensin-converting enzyme (ACE) level was abnormally high, and a needle aspiration biopsy showed non-caseating epithelioid cell granulomas. Surgical resection was performed, and the resected specimens showed irregularly shaped seminoma nests with intervening stroma consisting of epithelioid cell granulomas. Furthermore, immunohistochemistry demonstrated ACE expression in the epithelioid cells and some tumor cells. The patient's serum ACE level declined after the surgery and subsequent systemic chemotherapy, indicating the presence of tumor-induced sarcoid-like reactions rather than the coexistence of seminoma and sarcoidosis.