Adenocarcinoma arising in a tailgut cyst: report of a case.

We report herein the unusual case of a 66-year-old woman found to have adenocarcinoma arising in a tailgut cyst. The patient had been observed for 6 months following the discovery of a presacral cystic mass measuring 10 x 9 cm for which she had refused surgery. The serum tumor marker, carcinoembryonic antigen, became slightly elevated, and diagnostic imaging distinctly revealed a tumorous lesion with papillary projection into the cyst lumen. The cystic mass was then excised through the transsacral approach. The pathological findings were compatible with moderately differentiated adenocarcinoma arising in a tailgut cyst. This entity is extremely rare, and only six cases, including our own, have been reported in the English literature. Early complete excision is advised because it is almost impossible to determine for certain whether presacral cystic masses are benign or malignant prior to surgery.