A case with focal positivity of TTF1. Histologically, the tumor cells do not show clear morphologic differentiation (A). The displayed TTF1 staining (B) should be evaluated as positive, thus the tumor is diagnosed as “NSCC, favor adenocarcinoma”.
Another case with unclear morphologic differentiation (C). As the definition of a positive reaction with p40 is defined as 50% or more positive staining of the tumor cells, the widely scattered but sparse positive reaction with p40 (D) should not be considered as a definite diagnosis of squamous cell carcinoma (D).