Predictors of survival after resection of retroperitoneal sarcoma: a population-based analysis and critical appraisal of the AJCC staging system.

OBJECTIVE: To identify predictors of survival after resection of retroperitoneal sarcoma (RPS) and to evaluate the performance of the American Joint Committee on Cancer (AJCC) staging system for RPS. SUMMARY BACKGROUND DATA: Previous studies of survival after RPS resection are restricted to at most several institutions, yet the current AJCC staging system for RPS is based entirely on these relatively small studies.
METHODS: Patients undergoing resection of primary RPS from 1988 to 2005 were identified from the Surveillance, Epidemiology, and End Results (SEER) database. Cox proportional hazards models were used to analyze survival and evaluate AJCC staging.
RESULTS: In 1365 patient undergoing resection of primary RPS, the most prevalent histologies were liposarcoma (50%), leiomyosarcoma (26%), and malignant fibrous histiocytoma (11%). Median, 5-year, and 10-year survival after resection were 55 months, 47%, and 27%. Histological subtype (P < 0.001), histological grade (grade 3-4 vs. grade 1; HR, 2.42; P < 0.001), and tumor invasion of adjacent structures (HR, 1.37; P < 0.001) were associated with survival on multivariable analysis. However, tumor size had no prognostic value. Consequently, the AJCC T classification system demonstrated poor discriminatory ability (c = 0.50). The AJCC stage grouping system demonstrated moderate discriminatory ability (c = 0.66) but performed no better than a much simpler system that omits information on tumor size and lymph node metastasis (c = 0.67).
CONCLUSIONS: Indicators of tumor aggressiveness (histological grade and invasion of adjacent structures) as well as histological subtype predict survival after RPS resection. Tumor size, however, does not impact survival. The AJCC staging system for RPS is in need of revision.