This represents a special site of sarcoma (10% of cases). Management has similarities to soft tissue sarcoma of the chest wall or extermity, but the proximity to numerous critical structures and different natural history makes clinical decisions more complicated.
Diagnosis
Due to the location of the retroperitoneum, many patients do not develop symptoms until tumours are quite large; some patients may self detect an abdominal mass before they have developed any other symptoms. Most tumours are larger than 15 cm at diagnosis. Local symptoms may be present. Metastatic disease is present at diagnosis in about 10% of patients.
Important differential diagnoses include lymphoma, extragonadal germ cell tumours, metastatic disease (germ cell or gastrointestinal malignancies), Castleman's disease or retroperitoneal fibrosis.
Tissue Diagnosis
Tissue diagnosis should be performed unless the diagnosis is certain on imaging (usually only possible for well differentiated liposarcoma as this gives a characteristic fat density mass on CT/MRI that is locally invasive). There is a risk of disease seeding the biopsy tract but neoadjuvant therapy is difficult to deliver with no histology.
Staging
Staging is best done with local CT or MRI (to establish extent of local disease) and PET scan (to establish the presence of distant metastases).
Management
Surgery
Surgery is the primary treatment in all cases unless tumours are unresectable. Unresectable tumours invade vessels, the superior mesenteric vessels or the spinal cord; they are also considered unresectable if distant metastases or transcoelemic metastases have developed. Surgery should be the primary treatment if the tumour is low grade and resection would be uncomplicated as radiotherapy has minimal role for this disease. For patients with intermediate or high grade sarcoma, or if resection is borderline, neoadjuvant therapy should be administered.
Radiotherapy
Neoadjuvant radiotherapy has many potential advantages over adjuvant therapy. Planning is more straightforward with neoadjuvant therapy as the GTV is easily contoured and displaces critical structures out of the field; adjuvant therapy requires delineation of a CTV based on the pre-operative imaging and surgical findings. The small bowel should be more mobile in the pre-operative patient, preventing fixed loops from receiving the full dose of radiation. It may also allow for conversion of an unresectable tumour to a resectable tumour.
This has been shown in non-randomised studies; adjuvant radiotherapy improves local control but does not impact on overall survival. Neo-adjuvant studies have shown overall survival rates of 60-65%, better than the historical surgery-alone rates of 50%, although this may have been biased by patient selection.
Chemotherapy
There are no randomised studies comparing chemoradiotherapy to radiotherapy alone in the neoadjuvant setting and although promising non-randomised series have been published this is not a standard of care. Adjuvant chemotherapy is likewise controversial as there are conflicting results from randomised trials. Individualised treatment for patients is common based on their other risk factors, concurrent medical problems and wishes.
Outcomes
Most patients will recur locally.
