Diagnostic Challenge Pathology for Neurosurgery & Neurology Residents Department of Pathology University of Oklahoma Health Sciences Center, Oklahoma City, OK, U.S.A. Online Slide Case 4 History: The patient was a 50 year-old woman who was in good health until breast cancer was discovered about a year ago. Shortly after, a parietal ring enhancing mass was discovered and she was referred to the neurosurgery service. Contributor: Kar-Ming Fung, M.D., Ph.D., Last updataded:

MRI T1-Contrast A solitary parietal lobe lesion with an enhancing rim associated with substantial edema is present. MRI T2

The cells have large nuclei, prominent nucleoli, and substantial variation in nuclear size. Also present are multiple large cytoplasmic vacuoles. This type of vacuoles (arrow) are rather common in mucin producing adenocarcinoma. Cytologic Preparation

N Frozen Section There is extensive gland formation with mucin production (arrow) and necrosis (N).

N Permanent Section There is extensive necrosis (N). The tumor (arrow) is well demarcated from the surrounding brain parenchymal tissue (B). Metastatic carcinoma and melanoma are usually well demarcated from the residual brain parenchymal tissue. B

GCDFP-15 Permanent Section The tumor cells have large nuclei and prominent nucleoli. Immunohistochemistry: GCDFP-15 (+), TTF-1 (-), CK7 (+), CK20 (-).

What is your diagnosis?

Diagnosis: Metastatic adenocarcinoma of breast origin. Discussion: The history and the imaging clearly suggest a metastatic carcinoma. Most metastasis to the brain are of pulmonary origin. Histologically, carcinoma cells like to stay in clusters and are well demarcated from the residual brain tissue. Necrosis is often, but not always, present and may be extensive enough that only a small amount of viable tumor cells are present. The following immunohistochemical profile is compatible with breast origin. GCDFP15 is often positive in breast adenocarcinoma and TTF1 is positive in most pulmonary adenocarcinoma. The results on CK7 and CK20 do not help to distinguish one from the other. Thyroid transcription factor 1 (TTF-1): Negative. Gross cystic disease fluid protein 15 (GCDFP15): Positive CK7: Positive, CK20: Negative The interesting feature of this case is the substantial mucin production which is not a very common feature in metastatic breast adenocarcinoma.