Malignant teratoma of the thyroid with primitive neuroepithelial and mesenchymal sarcomatous components.
A 15-year-old black girl had a near total resection of a malignant thyroid teratoma with bilateral nodal involvement and mediastinal extension. A predominant neuroepithelial pattern had ependymal rosettes and mitoses, stained for neuron-specific enolase, neuron-specific B tubulin, and synaptophysin. A malignant spindle cell component stained for smooth-muscle actin, muscle actin, and to a lesser extent S-100. Loose myxoid tissue resembled primitive cartilage. Epithelial membrane antigen and cytokeratin identified epithelial foci. Chromogranin A, MIC2, glial fibrillary acidic protein, and thyroid stimulating hormone receptor stains were negative. There was focal anaplasia. DNA ploidy by laser scanning cytometry was 1.2. The tumor from the left and right thyroid lobes exhibited trisomy 8, the right also had hyperdiploid cell lines. She was treated with aggressive combination chemotherapy and radiation. Presently there is no residual disease 16 months after diagnosis. Malignant thyroid teratoma is an aggressive tumor, with 15 of 27 reported patients dying 2 weeks to 3 years after diagnosis. Survivors have been treated with total or subtotal resection, combination chemotherapy with agents effective in the treatment of germ cell tumors as well as sarcomas, and radiation for either recurrent or residual disease. The heterologous elements, lacking MIC2 staining and t(11;22), support the diagnosis of malignant teratoma rather than a neuroepithelial tumor. Trisomy 8 is the first cytogenetic abnormality described in malignant thyroid teratoma. Therapy should be tailored to the management of all transformed histologies.