A Case of Malignant Peripheral Nerve Sheath Tumor with Rhabdomyoblastic Differentiation: Malignant Triton Tumor
A 24-year-old man presented with a subcutaneous mass in his right thigh, which gradually enlarged over 8 years, then grew rapidly 1 year prior to consultation. His medical and family histories were unremarkable. Physical examination revealed a firm, movable, painless, subcutaneous mass measuring 10 × 8 × 7 cm (fig. ). Palpation revealed no inguinal lymphadenopathy. The patient presented neither cafe-au-lait spots nor cutaneous neurofibromas. T2-weighted magnetic resonance imaging revealed a solid, subcutaneous mass containing a cystic lesion (fig. ). Computed tomography of the chest, abdomen and pelvis showed no evidence of metastasis. The tumor was totally excised under general anesthesia, with a 3-cm margin including the muscle surface. The resected margins were clear.\nThe resected tumor was not connected to the nerve tissue. Histopathological examination revealed the tumor's tissue origin as well as cystic degeneration and central necrosis. In 1 region, the tumor was composed of spindle cells occurring among collagen bundles or in a loose fibromyxoid stroma corresponding to a neurofibroma (fig. ). Elsewhere, it was composed of spindle cells with hyperchromatic nuclei, together with some rounded or oval and strap-like cells possessing deeply eosinophilic cytoplasm in variably interlacing fascicles or whorls with a herringbone appearance or nuclear palisadings (fig. ). Mitoses were also observed (fig. ).\nImmunohistochemically, the majority of spindle cells intensely expressed S-100. Cells with deeply eosinophilic cytoplasm are often positive for desmin (fig. ). The MIB-1 (Ki-67) labeling index was less than 1% in the region corresponding to the neurofibroma, but had increased to 25% in the most mitotically active portion of the tumor. Postoperative radiation therapy was administered to the affected area. However, the patient died of brain and lung metastases 10 months after surgery.