Encapsulated anaplastic thyroid carcinoma without invasive phenotype with favorable prognosis: report of a case.

We herein report a case of anaplastic thyroid carcinoma in a 77-year-old woman with long-term disease-free survival. The tumor measured 7.5 x 6.0 cm in size and was diagnosed to be anaplastic carcinoma. We investigated the biological aggressiveness of this carcinoma by means of immunohistochemistry and found it have a high cell-proliferating activity, a disruption in the mechanism of apoptosis, and a high potential of cell spreading, similar to that observed in usual anaplastic carcinomas. The only unique point was that this tumor was encapsulated and no invasion of carcinoma cells beyond the capsule was microscopically observed. To avoid an obstruction of the trachea, a lobectomy without lymph node dissection was performed as a "palliative operation." Although neither adjuvant chemotherapy nor radiotherapy was carried out due to her age, she has nevertheless survived with no evidence of recurrence for 57 months after surgery. The presence of such a type of anaplastic carcinoma should thus be noted by surgeons and pathologists, even though the occurrence of such cases seems to be very rare.