Carcinoma of the thyroid with a mixed medullary, papillary, follicular, and undifferentiated pattern.

While papillary and follicular thyroid carcinomas are frequently mixed, this is a case of a medullary, papillary, follicular, and undifferentiated carcinoma of the same gland. In addition, all four tumor types were metastatic to regional lymph nodes. The patient described herein did not demonstrate features of the multiple endocrine neoplasia type 2 syndrome. Immunoperoxidase staining for calcitonin and thyroglobulin was positive in the follicular and medullary areas of tumor. Because the embryologic origin of the thyroidal follicular cells is from the endoderm and the origin of the parafollicular cells of the medullary carcinoma is from the ectodermal neural crest, this case seems noteworthy for demonstrating mixed metastatic tumor of composite embryologic origin. Alternatively, this case may represent an extension of what has recently been termed differentiated thyroid carcinoma, intermediate type by Ljungberg and co-workers.