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Gross Description: The specimen was taken from the lung and received in formalin. It consists of multiple cores; the longest measuring 1.2 cm. All submitted in one block.
Microscopic: PAS-positive, diastase-resistant, intracytoplasmic crystals and granules and intracytoplasmic glycogen are present to variable degrees. Nuclear pleomorphism is usually mild and mitotic activity low. Vascular invasion is identified in nearly all cases.
Immunohistochemistry Profile: TFE3: strong and diffuse nuclear positivity. PAS (special stain): positive for intracytoplasmic structures. S100, Pan CK, CK-MNF, CK 8/18, Inhibin, HEPBAR, HMB45, EMA, lysozyme, and PAX-8: Negative.
Differential Diagnosis:
- metastatic clear cell renal cell carcinoma is positive for EMA, CD10, and RCC and negative for TFE3
- melanoma is positive for S-100, HMB-45 and melan-A
- paraganglioma is positive for chromogranin and Synaptophysin
- granular cell tumour is positive for S–100
- clear cell sarcoma is positive for S-100, HMB-45, and melan–A
Diagnosis: Alveolar soft tissue sarcoma