Answer: Invasive adenocarcinoma of lung

Histology:

Discussion: Sections show sheets of tumor cells surrounded by fibrosis. At the periphery of the tumor atypical cells exhibit lepidic growth pattern along thickened/fibrotic alveolar septae. The solid component is composed tumor cells that have round to oval nuclei with clear chromatin and prominent nucleoli and eosinophilic cytoplasm with occasional intracytoplasmic clear vacuoles. The atypical cells growing along the alveolar septae have numerous intranuclear inclusions and show nuclear crowding/overlapping. Immunohistochemical stains show the tumor to be positive for CK7 and lung adenocarcinoma markers (TTF1 and Napsin-A), and focally and weakly positive for GATA-3. This immunohistochemical profile supports a primary adenocarcinoma of the lung. The staining is similar in both the solid and lepidic component of the tumor.

Metastatic urothelial carcinoma can pose a diagnostic difficulty in lung biopsies given the histologic overlap with primary lung tumors, particularly squamous cell carcinoma. Most commonly used immunostains can be positive in both urothelial and squamous cell carcinoma and therefore there is need for additional markers. GATA-3 is a new marker that is positive in the majority of urothelial carcinomas (UC) including 80% of high grade UC. In contrast, no GATA3 expression was found in lung squamous cell carcinomas and high grade prostatic adenocarcinomas. Focal mild staining can be seen in benign prostatic glands and in lung adenocarcinomas. Other tumors that are GATA-3 positive include carcinomas of the breast and skin appendage.

Reference(s):
– Chang et al. Utility of GATA3 immunohistochemistry in differentiating urothelial carcinoma from prostate adenocarcinoma and squamous cell carcinomas of the uterine cervix, anus, and lung. Am J Surg Pathol. 2012 Oct;36(10):1472-6.