Myxoepithelioid tumor with chordoid feature: A clinicopathological, immunohistochemical, and genetic study of 14 cases of SMARCB1/INI1-deficient soft-tissue neoplasm.

AIMS Complete loss of SMARCB1/INI1 in soft-tissue tumors such as malignant rhabdoid tumor, epithelioid sarcoma, myoepithelial tumor of soft tissue, and extraskeletal myxoid chondrosarcoma is often associated with high-grade malignancy and poor prognosis. The diagnosis is sometimes challenging due to histological similarities, so careful differential diagnosis is required. Therefore, soft-tissue tumors with complete SMARCB1/INI1 loss could potentially include an unknown entity. METHODS AND RESULTS We analyzed 160 cases of SMARCB1/INI1-deficient soft-tissue tumor and found 14 cases of tumors not classifiable into already existing categories and having common clinical and histological features. These involved 2 male and 12 female patients, ranging in age from 20 to 61 years. The tumors were located in the the pubo-inguinal region (n=13) and pelvic cavity (n=1). Histologically, the tumors showed relatively uniform epithelioid to spindle-shaped cells with myxoid stroma. All tumors showed immunoreactivity for brachyury, EMA, and PgR, while 12 of 14 cases did for ER. Variable positive staining for alpha-SMA, S-100 protein, and GFAP was seen. NR4A3 and EWSR1 gene rearrangements were not detected in 13 and 11 examined cases, respectively. Clinical follow-up data in the 14 patients showed 13 alive without disease and 1 lost to follow-up; 4 cases developed local recurrence and/or metastases. CONCLUSION The designation "myxoepithelioid tumor with choroid feature" (METC) was proposed as a tumor with intermediate malignancy controllable by appropriate treatment, including the entity of myoepithelioma-like tumor of the vulvar region. METC is a novel and independent subset histologically, biologically, and clinically distinct from already existing SMARCB1/INI1-deficient soft-tissue tumors.