Papillary carcinoma arising in a papillary cystadenoma of thyroid: a case report.

Papillary cystadenoma of the thyroid is a controversial pathologic entity, the existence of which is not universally accepted. Its malignant potential is unknown, with only scant evidence that it may be a rare precursor of the papillary carcinoma. A case is presented as a pathologically documented instance of malignancy arising in a papillary cystadenoma in a 33-year-old woman. The clinical implications of this finding are discussed.