Simultaneous occurrence of a medullary and a papillary thyroid carcinoma in the same patient.

We present the case of a patient in whom we diagnosed two different thyroid carcinomas (one on each lobe) of distinct histologic type: one derived from the follicular cells (papillary) and one from the C cells (medullary). They were both diagnosed preoperatively by fine needle aspiration (FNA), and the diagnosis was confirmed with histologic examination. "Inappropriate" staining with neuroendocrine markers was observed in the papillary tumor. Analysis of tumor tissue for the RET oncogene mutations, commonly found in the MEN2 syndromes, was negative. This case supports the view of a common origin for these two tumor types.