1. Diagnostic Challenge Pathology for Neurosurgery & Neurology Residents Department of Pathology University of Oklahoma Health Sciences Center, Oklahoma City, OK, U.S.A. Case 23 History: A 65 year-old man presented with a frontal-parietal lobe intra-axial tumor. The patient has a mass removed from the lung a few years before. Contributor: Kar-Ming Fung, M.D., Ph.D., karming-fung@ouhsc.edu Last updataded: 1/9/2009karming-fung@ouhsc.edu

2. Paraffin Section

3. CK7 CK5/6TTF-1 CK20 The tumor cells are negative for mucicarmine stain.

4. What is your diagnosis?

5. Diagnosis: Metastatic squamous cell carcinoma compatible with pulmonary origin. Discussion: The tumor cells have large, round nuclei with prominent nucleoli. The cells have a moderate to large amount of cytoplasm. The diagnostic feature is the polygonal shape of the cell with well defined cytoplasmic membrane and a gap between cells (arrow in the image on the right) Obviously, this is a metastatic tumor of non-small cell type. The more common differential diagnoses include metastatic malignant melanoma, squamous cell carcinoma and adenocarcinoma. The morphologic feature, especially the delicate gap between tumor cells suggest squamous cell carcinoma. The negative result for mucicarmine, positive CK5/6 immunoreactivity favor squamous cell carcinoma. CK7(+) and CK20(-) are compatible with pulmonary origin. Although TTF-1 are often positive in pulmonary adenocarcinoma and small cell carcinoma, they are typically negative for squamous cell carcinoma.