MACROSCOPIC DESCRIPTION: 1. "Posterior fossa cystic met": A fragment of soft pink and gelatinous tissue 4mm, for frozen section/smear. FS DIAGNOSIS: Metastatic carcinoma  2. "Posterior fossa cystic met": Two pieces of soft pink tissue 14x7x5mm and 13x5x8mm. The larger piece is bisected.

MICROSCOPIC DESCRIPTION:1,2. The sections show a densely cellular malignant tumour, forming thickened solid trabeculae with areas of necrosis. The tumour cells are basaloid in appearance with high N/C ratio, enlarged hyperchromatic nuclei, small nucleoli and scanty cytoplasm. There are scattered mitoses. No evidence of lymphovascular invasion is seen. The tumour cells are CK7 and c-kit positive. About 20% of the cells are weakly positive for oestrogen receptor. GATA-3, PR, HER2 and TTF-1 are negative. The features are consistent with metastatic adenoid cystic carcinoma (solid pattern).

DIAGNOSIS: 1,2. Posterior fossa: Metastatic adenoid cystic carcinoma, consistent with breast primary.

SUPPLEMENTARY REPORT: This tumour shows similar morphology as to the previous breast lesion. The breast lesion is also c-kit positive.

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