MICROSCOPIC DESCRIPTION: Paraffin sections show fragments of fibrovascular tissue in which there is extensive necrosis and infiltration by a densely hypercellular tumour. Tumour cells have pleomorphic angulated hyperchromatic nuclei and a small amount of cytoplasm and are arranged in small solid polygonal and single-file aggregates within a dense fibrous stroma. Moderate numbers of mitotic figures are noted. Tumour cells form cuffs around small calibre arteries and veins. Several of these show complete lumenal obliteration by endarteritis.
Immunohistochemistry shows strong cytoplasmic staining in tumour cells for cytokeratin CK7 and weaker staining for cytokeratin CK5&6. No staining for TTF-1, E-cadherin, oestrogen receptor (ER), progesterone receptor (PgR), HER-2 or GCDFP is seen. The features are of metastatic non-small cell carcinoma most consistent with an origin from lung.
DIAGNOSIS: Brain tissue: Metastatic non-small cell carcinoma with features most consistent with an origin from lung.