Role of thyroid transcription factor-1 in the diagnosis of feline lung-digit syndrome

Objectives The aim of this study was to investigate the role of thyroid transcription factor-1 (TTF-1) in the diagnosis of feline lung-digit syndrome (FLDS) and to investigate the associations between the morphological features of FLDS and TTF-1 expression. We also compared the reliability of TTF-1 and transmission electron microscopy (TEM) in establishing the diagnosis of FLDS. Methods Histology records of feline digit tumours were retrieved, including patients from 2008-2015. If formalin-fixed, paraffin-embedded tissues were available for review, patients were included in the study. As a control group we included 12 feline primary tumours of the digits. All the histological slides of the study group were blindly reviewed by the same veterinary pathologist. Representative sections of the lesions were selected for immunohistochemistry (IHC) analysis. To confirm the respiratory origin of the neoplastic tissue, TEM was used as a gold standard in all cases. Results Five cases of FLDS were included. TTF-1 was weakly to moderately positive in 60% of the cases, showing no correlation with the microscopic presence of ciliated epithelium. When IHC results were combined with the presence of cilia, 80% of the cases from the study group could be identified as FLDS. TEM confirmed the presence of ciliated epithelium in all five cases, confirming the respiratory origin of the neoplastic tissue and therefore the diagnosis of FLDS. Conclusions and relevance TTF-1 expression is maintained in FLDS. While the combination of TTF-1 and identification of cilia confirms FLDS, TEM should be considered in those cases where diagnosis is uncertain and FLDS is suspected.