Soft tissue sarcomas (STS) are derived from mesenchymal cells, and can arise at any site. Retroperitoneal sarcomas (RPS) account for \~15% of STS, and patients have much worse survival outcomes than for extremity STS. Local (abdominal) recurrence of RPS is very common, due to the challenges of obtaining complete resection of these large masses that abut critical central compartment structures, such as the inferior vena cava and aorta. There is currently intense interest in using preoperative therapy to downsize/cytoreduce RPS and hopefully improve oncologic outcomes. Studies have shown that preoperative radiation does not cytoreduce these tumours. In this study, the potential of systemic therapy for cytoreduction will be examined.
The standard systemic therapy regimen for treatment of patients with STS remains Adriamycin/Ifosphamide, although side effects can be tolerated only by relatively young and fit patients. The use of this regimen preoperatively for extremity STS results in average response rates of about 30-40%, as judged by histologic assessment of the resected specimen. The international experience with preoperative chemotherapy for RPS is very limited, and there are no published reports.
Functional imaging may provide a more meaningful assessment of tumour response to systemic therapy. PET-MR is a newer modality that may hold promise in assessing solid tumour response and its potential utility is currently of rapidly growing interest. Conventional MRI can offer a more detailed assessment of tumour relationships to adjacent structures than can CT, particularly in STS. Integration of PET with MR has the potential to provide information about metabolic tumour volume (MTV) and to help guide surgical planning.There are no data available on the utility of PET-MR in evaluating tumour response to chemotherapy in STS.
At present, the role of chemotherapy as a preoperative treatment for retroperitoneal sarcoma (RPS) is undefined and controversial. The sarcoma group at Princess Margaret Cancer Centre (PMCC) has had some experience with this treatment paradigm, but like most sarcoma groups in Ontario, and Canada, has reserved preoperative chemotherapy for frankly unresectable and borderline resectable tumours for which downsizing would potentially render resection more feasible. At present, CT-scan imaging is performed after 2 cycles of chemotherapy, and if there is no frank progression of the cancer, chemotherapy is continued for another 3-4 cycles. By that point the tumour is smaller on CT scan in about 30% of patients. There are 2 main problems with this approach: 1)70% of the patients may have undergone 5-6 cycles of chemotherapy with no apparent benefit; and 2) there may be a metabolic response and associated benefit without a change in tumour size. The ability to reliably assess tumour response earlier on (i.e. after 1 cycle) would significantly influence the care of these patients as ineffective chemotherapy could be terminated after 1 cycle and the regimen could be modified, or surgery could happen right away before the window of resectability is lost.
