[Age-related Epstein-Barr virus-associated lymphoproliferative disorder presenting as rapidly developing renal mass]

An 83-year-old man visited our department with a slightly enhanced mass of about 2 cm in diameter, detected incidentally in the left kidney on computed tomography (CT) performed for other reasons in a different department. Fluorodeoxyglucose-positron emission tomography was performed under the suspicion of metastatic renal tumor and malignant lymphoma. Accumulation was observed in the mass but not in other regions. The tumor size was about 2 mm on CT 4 months previously, indicating rapid enlargement. Based on these observations, a malignant renal tumor was diagnosed and laparoscopic left nephrectomy was performed. Pathologic examination revealed relatively large cells diffused within a background of many small lymphocytes and histiocytes. The large cells were positive when tested by Epstein-Barr virus (EBV)-encoded RNA in situ hybridization. No clinically apparent immunodeficiency was observed, suggesting age-related EBV-associated lymphoproliferative disorder caused by an underlying age-related reduction in immunocompetence. This is the first report of a kidney-localized case in Japan.