Histology (cerebellar lesions)

MICROSCOPIC DESCRIPTION: All the sections show features of metastatic undifferentiated large cell carcinoma, infiltrating into the cerebellar parenchyma. The tumor forms nodules and solid sheets. No specific lines of differentiation are identified. There are areas of necrosis. The tumor cells appear squamoid in appearance with enlarged nuclei, prominent nucleoli and abundant pale eosinophilic-to-clear cytoplasm. However, keratinization is not present. Lymphovascular invasion is not seen. Immunostains are to follow.

DIAGNOSIS: Multiple foci of metastatic undifferentiated large cell carcinoma.

SUPPLEMENTARY REPORT: The tumor cells are diffusely positive for CK5/6 and p63. There is focal staining for CK7 and CK14. About 5% of the cells are positive for ER (2+). PR is negative. More than 10% are positive for HER2 (2+, equivocal). CK20, TTF-1, GCDFP15 and p16 are negative. The results are difficult to interpret. Breast carcinoma (with basal-like phenotype) is a possibility. CK5/6 and p63 may be seen in squamous cell carcinomas. Lung or cervical primary would also be in the differential.