The patient went on to have a biopsy (of a brain metastasis - not shown)
MICROSCOPIC DESCRIPTION: The section shows fragments of densely hypercellular, moderately differentiated adenocarcinoma. This consists of moderately well-formed glandular structures lined by a stratified arrangement of pleomorphic cuboidal and columnar epithelial cells. Areas with a solid arrangement of tumor cells are also noted. Frequent mitotic figures are identified and there are foci of tumor necrosis.
Immunohistochemistry shows strong cytoplasmic staining in tumor cells for cytokeratins CK7 and BerEp4. No staining for TTF-1, carcinoembryonic antigen (CEA), CDX-2 or cytokerartins CK 5&6 and CK20 is seen in tumor cells. This profile favors an origin of tumor from lung.
DIAGNOSIS: Metastatic moderately differentiated adenocarcinoma from lung.