Thyroid transcription factor‐1 is the superior immunohistochemical marker for pulmonary adenocarcinomas and large cell carcinomas compared to surfactant proteins A and B

Aims Antibodies against the thyroid transcription factor‐1 (TTF‐1) and the surfactant proteins A and B (SPA, SPB) were compared as paraffin‐reactive immunohistochemical markers for non‐small cell carcinomas of pulmonary origin. Methods and results We studied 138 carcinomas of pulmonary origin (98 adenocarcinomas, 20 non‐neuroendocrine large cell carcinomas, 20 squamous cell carcinomas) and a total of 276 extrapulmonary carcinomas of various primary origins. Using the monoclonal antibody 8G7G3/1, TTF‐1 was detectable in 75% of non‐mucinous pulmonary adenocarcinomas and in 40% of large cell carcinomas but in only 10% of mucinous adenocarcinomas and not in squamous cell carcinomas. In contrast, both SPA and SPB were positive in only 45% of pulmonary adenocarcinomas and in 10% and in 5% of the large cell carcinomas, respectively. TTF‐1 had a specificity of 0.98 for pulmonary carcinomas as 5/7 thyroid carcinomas were the only TTF‐1‐positive extrapulmonary tumours. Anti‐SPB and anti‐SPA had specificities of 1.00 and 0.97, respectively. Conclusions The monoclonal antibody 8G7G3/1 against TTF‐1 should be the first choice as a component of an antibody panel aiming to prove or to exclude the pulmonary origin of non‐mucinous adenocarcinomas and non‐neuroendocrine poorly differentiated carcinomas, especially in patients presenting with metastatic carcinomas of unknown primary site.