Immunostaining for thyroid transcription factor 1, Napsin A, p40, and cytokeratin 5 aids in differential diagnosis of non-small cell lung carcinoma.

The present study aimed to examine the effectiveness of immunostaining of cytological specimens in discerning squamous from non-squamous cell carcinoma. Various combinations of six antibodies were examined in order to determine the optimal combination for use in differential diagnosis. Immunostaining was performed using tumor imprint smears obtained from 70 lung carcinoma cases. The results were scored based on positive area and intensity. For objective evaluation, scores for thyroid transcription factor 1 (TTF-1), napsin A, and CK CAM5.2 were expressed with positive values, while those for p40, cytokeratin (CK) 5/6 and CK5 were expressed with negative values. Histograms were produced to evaluate which combination was the most effective in differentiating squamous cell carcinoma from adenocarcinoma. The sensitivity for these molecules in adenocarcinoma was 88% for TTF-1, 85% for napsin A, and 100% for CAM5.2. In squamous cell carcinomas, sensitivity was determined to be 90% for p40, 86% for CK5, and 76% for CK5/6. The specificity for these molecules was calculated as 100%, 95%, 43%, 98%, 100% and 95%, respectively. Each combination was evaluated for scoring and the values were averaged. The most effective combination for mode and mean was TTF-1, napsin A, p40, and CK5, for which all adenocarcinomas had a score >1, and all squamous cell carcinomas scored <-2. Immunostaining scoring may therefore be useful for the differential diagnosis of these carcinomas when a limited number of tumor cells are present.