Extrarenal (extracranial) rhabdoid tumor
Malignant rhabdoid tumors were first described in children with renal tumors in 1981 (refer to the Wilms Tumor and Other Childhood Kidney Tumors Treatment summary for more information) and were later found in a variety of extrarenal sites. They are uncommon and highly malignant, especially in children younger than 2 years. The first sizeable series of 26 childhood patients with extrarenal extracranial malignant rhabdoid tumor of soft tissues came from patients enrolled on the Intergroup Rhabdomyosarcoma Studies (IRS) I through III during a review of pathology material. Only five patients (19%) were alive without disease. Later, investigation of children with atypical teratoid/rhabdoid tumors of the brain, as well as those with renal and extrarenal malignant rhabdoid tumors, found germline and acquired mutations of the SMARCB1 gene in all 29 tumors tested. Rhabdoid tumors may be associated with germline mutations of the SMARCB1 gene and may be inherited from an apparently unaffected parent. This observation was extended to 32 malignant rhabdoid tumors at all sites in patients whose mean age at diagnosis was 12 months. The disease can occur congenitally  and is uncommon in older children and adults.
In a Surveillance Epidemiology and End Results study of 229 patients with renal, central nervous system, and extrarenal malignant rhabdoid tumor, patients aged 2 to 18 years, limited extent of tumor, and delivery of radiation therapy were shown to affect the outcome favorably compared with other patients (P < .002 for each comparison). Site of the primary tumor was not prognostically significant. Overall survival at 5 years was 33%.
Treatment includes surgical removal when possible, chemotherapy as used for STSs (but no single regimen is currently accepted as best), and radiation therapy.[Level of evidence: 3iA]; [113,114][Level of evidence: 3iiiB]
Extraskeletal myxoid chondrosarcoma
Extraskeletal myxoid chondrosarcoma is relatively rare among STSs, representing only 2.3% of all STSs. It has been reported in children and adolescents.
Extraskeletal myxoid chondrosarcoma is a multinodular neoplasm. The rounded cells are arranged in cords and strands in a chondroitin sulfate myxoid background. Several cytogenetic abnormalities have been identified (see Table 2), with the most frequent being the translocation t(9;22)(q22;q12), involving the EWSR1/NR4A3 genes. The tumor has traditionally been considered of low-grade malignant potential. However, recent reports from large institutions showed that extraskeletal myxoid chondrosarcoma has significant malignant potential, especially if patients are followed for a long time.[119,120] Patients tend to have slow protracted courses. Nodal involvement has been well described. Local recurrence (57%) and metastatic spread to lungs (26%) have been reported.
The therapeutic benefit of chemotherapy has not been established. Aggressive local control and aggressive resection of metastases led to OS of 87% at 5 years and 63% at 10 years. There may be potential genetic targets for small molecules, but these should be studied as part of a clinical trial.