Thyroid transcription factor 1 expression in cystic lesions of the neck: an immunohistochemical investigation of thyroglossal duct cysts, branchial cleft cysts and metastatic papillary thyroid cancer.

Cervical metastases of papillary thyroid cancer (PTC) are of particular diagnostic importance, because they can mimic branchiogenic cysts clinically and histopathologically when undergoing cystic change. Immunohistochemical stains for thyroid transcription factor 1 (TTF-1), which are positive in thyroid cancers, are reported to be valuable in establishing diagnosis. However, TTF-1 may also be expressed in dysontogenetic cysts of the neck. Therefore, immunohistochemical stains for TTF-1 and thyroglobulin (TG) were performed on each of the ten thyroglossal duct cysts, branchial cleft cyst and lymph node metastasis of PTC. Five in ten cases of thyroglossal duct cysts were positive for TTF-1, but all were negative for TG. One of the ten branchial cleft cysts stained for TTF-1, while all cases were negative for TG. All ten cases of lymph node metastases of PTC showed positive for TTF-1, nine of which were positive for TG. Since a positive immunostaining for TTF-1 in cystic lesions of the neck was not only found in metastases of PTC, but also in non-malignant branchiogenic cysts, additional investigations, e.g. an immunostaining for TG, should be added in difficult cases.