Greater than 90% tumor resection either at presentation or after neoadjuvant chemotherapy may be a favorable prognostic factor for overall survival.[93,94] Treatment may include chemotherapy, surgery, and radiation therapy. Multiagent chemotherapy analogous to that used for sarcomas has been used, as well as total abdominal radiation therapy.[88,89,93,95,96]
Epithelioid sarcoma is a rare mesenchymal tumor of uncertain histogenesis which displays multilineage differentiation. It is characterized by inactivation of the SMARC gene, which is present in both conventional and proximal types of epithelioid sarcoma.
Epithelioid sarcoma commonly presents as a slowly growing firm nodule based in the deep soft tissue; the proximal type predominantly affects adults and involves the axial skeleton and proximal sites. The tumor is highly aggressive and has a propensity for lymph node metastases.
In a review of 30 pediatric patients with epithelioid sarcoma (median age at presentation, 12 years), responses to chemotherapy were reported in 40% of patients using sarcoma-based regimens, and 60% of patients were alive at 5 years following initial diagnosis. A single-institution retrospective review of 20 patients, including children and adults, found no difference in the probability of recurrence between patients who received chemotherapy and those who did not receive chemotherapy and suggested that radiation therapy may be useful. Surgical removal of primary and recurrent tumor(s) was most effective.[Level of evidence: 3iiiA]
Perivascular epithelioid cell tumors (PEComas)
PEComas (tumors showing perivascular epithelioid cell differentiation) include the following:
Benign PEComas are common in tuberous sclerosis, an autosomal dominant syndrome that also predisposes to renal cell cancer and brain tumors. Tuberous sclerosis is caused by germline inactivation of either TSC1 (9q34) or TSC2 (16p13.3), and the same tumor suppressor genes are inactivated somatically in sporadic PEComas. Inactivation of either gene results in stimulation of the mTOR pathway, providing the basis for the treatment of nonsurgically curable PEComas with mTOR inhibitors.[102,103]
PEComas occur in various rare gastrointestinal, pulmonary, gynecologic, and genitourinary sites. Soft tissue, visceral, and gynecologic PEComas are more commonly seen in middle-aged female patients and are usually not associated with the tuberous sclerosis complex. Most PEComas have a benign clinical course, but malignant behavior has been reported and can be predicted based on the size of the tumor, mitotic rate, and presence of necrosis.