Mixed tumor of the soft tissue (arm)

Mixed tumor of soft tissue is extremely rare; only 15 cases have been reported in English literature. A 56-year-old man presented with a tumor in right arm. Physical examination showed a tumor measuring 3 × 3 × 3 cm of deep portion of right arm. MRI showed a well-defined deep tumor measuring 3 × 3 × 4 cm of arm next to fascia. The tumor was resected, and it was found that the tumor is located in deep subcutaneous tissue outside the fascia. Histologically, the tumor was well-defined and contained a fibrous capsule. The tumor cells showed no significant nuclear atypia. The tumor was composed of epithelial, myoepithelial, and stromal elements. The epithelial element formed tubules, and myoepithelial element showed solid nests and periepithelial linings. The epithelial element showed frequent apocrine features including apocrine snouts. The stromal element was composed of cartilage and myxoid tissues. Immunohistochemically, the epithelial element was positive for cytokeratin (CK) AE1/3, CK CAM5.2, CK34BE12, CK7, CK8, CK18, CK19, EMA, CEA, CD56, p53, and Ki-67 (labeling = 80%), but negative for CK5/6, CK14, CK20, vimentin, p63, S100 protein, CD10, CD34, ASMA, CD68, myoglobin, bcl-2, BMP-2, TGF-β1, CDK-4, and MDM2. The myoepithelial element was positive for CK AE1/3, CK CAM5.2, CK34BE12, CK5/6, CK7, CK8, CK14, CK18, p63, vimentin, CD10, S100 protein, bcl-2, p53, and Ki-67 (labeling = 20%), but negative for CK19, CK20, EMA, CEA, CD34, ASMA, CD68, CD56, myoglobin, BMP-2, TGF-β1, CDK-4 and MDM2. The stromal element was positive for vimentin, S100 protein (cartilage), and Ki-67 (labeling = 6%), but negative for other antigens examined including bcl-2, BMP-2, TGF-β1, CDK-4 and MDM2. No findings of metastasis, invasion, and recurrence were recognized clinically. The author speculates that the current mixed tumor was derived from misplaced apocrine glands in the deep soft tissue.