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RETROPERITONEAL LIPOSARCOMA: IS THERE A SURVIVAL BENEFIT TO ADJUVANT RADIOTHERAPY?
MJ Littau, P Kim, S Kulshrestha, C Bunn, C Tonelli, ZM Abdelsattar, FA Luchette, MS Baker
Loyola University Medical Center

Background
Retroperitoneal liposarcomas are typically low grade and present as large tumors in close proximity to multiple vital anatomic structures. Resection often results in one or more histologically positive margin. Adjuvant external beam radiation (aXRT) is a potential adjunct to resection but carries risk of injury to adjacent organs. Few studies evaluate the efficacy of aXRT in these indolent tumors.

Methods
We queried the National Cancer Database to identify patients undergoing surgical resection to microscopically positive (R1) margins between 2004 and 2016 for large (> 5cm) low and moderate grade retroperitoneal liposarcoma. Patients presenting with metastatic disease, those having high grade histology, and those receiving neoadjuvant or intra-operative radiation and/or adjuvant chemotherapy were excluded. Patients receiving aXRT were 1:2 propensity matched for age, demographics, comorbid disease, tumor size, grade, and pathologic stage to patients treated with resection alone. Kaplan Meier (KM) method was used to compare overall survival (OS) profiles for matched cohorts.

Results
476 patients met inclusion criteria. 370 underwent resection alone; 106 underwent resection followed by aXRT. On univariate comparison, patients receiving aXRT were more likely to be male (66% vs 53%, p = 0.023), more likely to have moderate grade histology (25.5% vs 16.5%, p = 0.050), and less likely to be treated in academic facilities (36.8% vs 59.2%, p < 0.001) than those undergoing resection alone. All 106 patients receiving aXRT were propensity matched to 212 undergoing resection alone. There were no statistical differences between matched cohorts with regard to age, demographics, comorbid disease, facility type, tumor size, grade, or stage. On KM analysis of the matched cohorts (Figure 1), there was no statistical difference in 5-year OS between patients treated with aXRT and those undergoing R1 resection alone (69.7% vs 76.8%, p = 0.53).

Conclusion
In patients undergoing R1 resection of large, moderate- and well-differentiated retroperitoneal liposarcoma, aXRT is not associated with an improvement in OS and should not be routinely offered as an adjunct to resection.


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