Neuroendocrine carcinoma in a mediastinal teratoma as a rare variant of somatic-type malignancy.

Somatic-type malignancy (STM), defined as any sarcoma, carcinoma, leukemia or lymphoma developing in a germ cell tumor, occurs in approximately 2% of all germ cell tumors. Neuroendocrine carcinoma developing in a mediastinal germ cell tumor has not been previously reported. We here describe a 22-year-old man who underwent resection of a 11-cm mediastinal teratoma which consisted of components of all three germ cell layers with prominent foci of fetal-like liver tissue. The liver areas were surrounded by primitive neuroendocrine structures with ductal and solid growth pattern with a high proliferation rate. We diagnosed an immature mediastinal teratoma with STM, specifically neuroendocrine carcinoma arising in a background of immature liver tissue. Comparative genomic hybridization of dissected tumor tissue revealed chromosomal gains at 12 in the teratoma and neuroendocrine carcinoma component. In summary, clinicians and pathologists should be aware of neuroendocrine carcinoma as a rare type of STM complicating mediastinal germ cell tumors.