[Biphasic sarcomatoid carcinoma of the thyroid: an exceptional localization of a rare tumor].

Thyroid sarcomatoid carcinoma is a rare and aggressive neoplasm composed of a follicular carcinoma which is contiguous or admixed with a pleomorphic spindle cell component. We report the case of a thyroid tumor reputed to have a poor outcome, in a 62-year-old woman. The radical thyroidectomy specimen was totally invaded. Results of immunoperoxidase staining for thyroglobulin and epithelial markers were positive in the areas of follicular carcinoma and negative in the sarcomatous component. The patient died a few days later due to septic shock. The epithelial and mesenchymal components of thyroid carcinosarcoma were both part of the neoplastic parenchyma and evolved from a single common stem cell, in agreement with the hypothesis that the tumors are of monoclonal origin. The definition of this tumor as its histogenesis and prognostic are discussed.