Solid adenocarcinoma of the lung consisting of solid sheets and anastomosing trabeculae. The dense eosinophilic cytoplasm creates a resemblance to squamous cell carcinoma. Solid adenocarcinoma of lung vs Squamous cell carcinoma: Solid adenocarcinoma will usually demonstrate at least focal presence of mucin with histochemical stains. In mucin-negative cases, the expression of pneumocyte markers (TTF-1 and/or Napsin A) is acceptable as evidence of solid differentiation. Solid adenocarcinoma also lacks diagnostic squamous features such as keratin pearls and intercellular bridges. Squamous cell carcinomas are positive for squamous markers such as p40 and p63 and negative for TTF1 and Napsin A.