TTF1 and squamous cell carcinoma: Squamous cell carcinomas usually exhibit pronounced keratinization and intercellular bridges and is diffusely positive for P63 and P40; adenocarcinomas are positive for TTF-1 and napsin-A; and neuroendocrine tumors are positive for CD56, synaptophysin, and chromogranin.[14] PLGA/PAC exhibited diverse growth patterns, without keratinization.