Metastatic mediastinal mature teratoma with malignant transformation in a young man with an adenocarcinoma in a Klinefelter's syndrome: Case report and review of the literature.

Malignant transformation of mediastinal mature teratoma is extremely rare and worsens the prognosis of the disease. Transformation can appear synchronously to or several years after the initial diagnosis. Clinical and radiological signs can orientate the clinician but the definitive diagnosis is obtained thanks to histology. An 11 year-old boy presented with a mediastinal mature teratoma and bone and pulmonary metastases. He received six cycles of chemotherapy combining etoposide, ifosfamide, cisplatin, followed by resection of a 16×14×9cm mediastinal mass. Karyotype analysis revealed the presence of an additional sex chromosome X (47 XXY) pathognomonic of Klinefelter's syndrome. Ten years later, sciatalgia revealed malignant transformation of a pre-existing sacral bone metastasis into gastrointestinal adenocarcinoma. The patient received four cycles of chemotherapy combining oxaliplatin, 5-fluorouracil and cetuximab. This treatment was followed by a complete resection of the sacral metastasis and completed with adjuvant irradiation of 54Gy in 30 daily fractions. Twelve months after the diagnosis of relapse, the patient remained alive without disease. To our knowledge, this is the first case of adenocarcinoma developed in bone metastases of a mediastinal mature teratoma in a boy with a Klinefelter's syndrome. We propose a review of the literature and an analysis of 20 others published cases of mediastinal teratoma with malignant transformation into adenocarcinoma.