[A Case of Primary Mediastinal Seminoma Showing Local Increase in Residual Tumor after Chemotherapy].

A 19-year-old man with abnormal findings on his chest X ray was referred to our hospital. A chest computed tomography scan revealed a 57 mm mass in the anterior mediastinum, and percutaneous needle biopsy was performed. Histopathological diagnosis was pure seminoma. Since the serum alphafetoprotein (AFP) level was normal and no abnormal findings were noted in the testis, the patient was diagnosed with mediastinal seminoma [International Germ Cell Consensus Classification (IGCCC) goodrisk group]. After three cycles of chemotherapy with bleomycin/etoposide/cisplatin [BEP], the tumor decreased in size to 32 mm, and a fluorodeoxyglucose-positron emission tomography scan indicated negative tumor findings. After four months, the residual tumor increased in size to 40 mm without any increase in the tumor marker levels. Surgical resection was performed, and the histopathological finding was only mature teratoma. Six months after the operation, there has been no recurrence.