Surgery With or Without Radiation Therapy in Treating Patients With Primary Soft Tissue Sarcoma of the Retroperitoneum or Pelvis

DISEASE CHARACTERISTICS: * Histologically confirmed primary soft tissue sarcoma of the retroperitoneum or pelvis (e.g., iliac fossa) * The following histologies are eligible: * Alveolar soft part sarcoma * Anaplastic sarcoma * Angiosarcoma * Atypical lipomatous tumor (low-grade liposarcoma) * Clear cell sarcoma * Epithelioid sarcoma * Fibrosarcoma * Leiomyosarcoma * Liposarcoma (all subtypes) * Malignant fibrous histiocytoma * Malignant peripheral nerve sheath tumor * Myxofibrosarcoma * Neurofibrosarcoma * Spindle cell sarcoma * Synovial sarcoma * Unclassified sarcoma * The following histologies are not eligible: * Rhabdomyosarcoma * Extraosseous Ewing's sarcoma * Primitive neuroectodermal tumor * Osteosarcoma * Chondrosarcoma * Aggressive fibromatosis (desmoid tumor) * Gastrointestinal stromal tumor * Sarcomatoid carcinoma * Hemangiopericytoma * Retroperitoneal sarcomas located predominantly in the retroperitoneum extending across the inguinal ligament into the abdominal wall are allowed provided that ≥ 90% of the tumor volume is located within the retroperitoneal space * No bowel obstruction OR history of previous bowel obstruction attributed to retroperitoneal tumor * Primary non-visceral retroperitoneal masses consistent with sarcoma allowed provided diagnoses of carcinoma, melanoma, and lymphoma are excluded by immunohistochemistry * Measurable gross disease by …