Our study examines thyroid transcription factor 1 (TTF-1) expression in 40 primary adenoid cystic carcinomas (ACCs) arising in various sites and compares TTF-1 expression between primary and metastatic ACCs in 12 cases with distant metastases.
Forty patients with ACCs, including 12 pairs of primary and metastatic ACCs, were evaluated for the immunohistochemical expression of TTF-1 (clone SPT24). In addition, 10 metastatic ACCs to the lung were tested on napsin A and a different TTF-1 antibody (clone 8G7G3) for further evaluation.
No primary ACCs showed TTF-1 immunoreactivity (clone SPT24). TTF-1 was positive in five (41.7%) of 12 metastatic ACCs; all five cases were found only in the lung and comprised five (50.0%) of 10 cases. In all positive cases, staining was focal and detected only in the cribriform histologic subtype. Staining patterns using both antibodies (both SPT24 and 8G7G3) were very similar, and TTF-1-positive tumor cells were also positive for napsin A. Extrapulmonary ACCs were all negative for TTF-1 regardless of origination and metastasis.
TTF-1- and napsin A-positive ACCs in the lung should not be considered primary ACCs because TTF-1 and napsin A can be expressed in metastatic ACCs of the lung.