Primary Thyroid Gland Alveolar Soft Part Sarcoma

Alveolar soft part sarcoma (ASPS) is a rare soft tissue tumor of unknown histogenesis generally characterized by the der(17)t(X;17)(p11.2;q25) translocation which results in the ASPSCR1-TFE3 gene fusion. Primary ASPS of the thyroid gland has not yet been reported. During oncology follow-up for breast cancer, a pulmonary nodule and thyroid gland mass were identified in a 71-year-old Korean male. Thyroid ultrasound showed a 5.7 cm left thyroid gland mass. After several fine needle aspirations, a thyroid gland lobectomy was performed after documenting only non-caseating granulomatous inflammation in a biopsy of the lung nodule. A 7.6 cm bulging nodular thyroid gland mass was identified, showing significant destructive invasion. Alveolar nests of large polygonal, eosinophilic, granular neoplastic cells were separated by vascularized stroma. Colloid was absent. Tumor necrosis and increased mitoses were identified. The neoplastic cells were positive with TFE3 and CD68, but negative with pancytokeratin, thyroglobulin, TTF-1, napsin-A, calcitonin, PAX8, CAIX, S100 protein, HMB45, SMA, and desmin. FISH confirmed a TFE3 gene rearrangement. The differential includes several primary thyroid gland epithelial neoplasms, paraganglioma, PEComa, melanoma, crystal storage disease, and metastatic carcinomas, especially Xp11 translocation renal cell carcinoma. The patient has refused additional therapy, but is alive without tumor identified (primary or metastatic).

Alveolar soft-part sarcoma: a review of the pathology and histogenesis

The descriptive designation, alveolar soft-part sarcoma, continues to be used for this uncommon soft-tissue malignancy because an acceptable hypothesis for its histogenesis has not been advanced, despite studies with electron microscopy and immunohistochemistry. These techniques have, nevertheless, provided significant information that is useful in the differential diagnosis of the tumor and pertinent in speculation concerning its nature. The most intriguing ultrastructural feature is the secretory process that culminates in the formation of the distinctive cytoplasmic crystals. Myogenic differentiation has been favored in a number of recent reports on the basis of immunohistochemical findings and the presence of the crystals does not rule out the possibility, but accounts of immunoreactivity for the myogenic regulatory protein MyoD1 have not been confirmed in subsequent studies or in the authors' own staining of six cases.