(P 216) LONG TERM SURVIVAL AND PROGNOSTIC FACTORS IN PATIENTS WITH PRIMARY RETROPERITONEAL LEIOMYOSARCOMA UNDERGOING SURGERIES: REAL WORLD DATA FROM A CHINA RETROPERITONEAL SARCOMA REFERRAL CENTER

Objective: Retroperitoneal leiomyosarcomas(RPLMS) represent rare heterogeneous malignancies. Radical R0/R1 surgical resection of sarcomas remains the mainstay of the treatment. Few data specifically reported the long-term oncological outcomes of primary RPLMS. We sought to discover the long-term progression-free survival (PFS), overall survival(OS) and its associated prognostic factors.

Methods: RPLMS patients who were first diagnosed and admitted to surgery in Peking University International Hospital from January 2015 through December 2019 were retrospectively reviewed. Patients with recurred LMS or LMS originating from the uterus, urinal or GI tracts were excluded. The primary endpoints were RFS and OS calculated using the Kaplan-Meier method. Prognostic factors were analyzed through the cox proportional hazard model. A p-value less than 0.05 was considered statistical significance.

Results: In total, 40 patients (11 male) met the criteria for inclusion. The Median follow-up time was 60 months (range 2-79 months). Liver or lung metastases were found in 6(15%) patients preoperatively. Systemic therapy was administered in 25%(10/40) of patients during the entire course of treatment. R0/R1 resection was achieved in up to 97.5%(39/40) of patients with an en-block resection rate of 77.5%(31/40). The Median PFS and OS were 15months, 48months, respectively. The 1-year, 3-year, 5-year PFS and OS were 51.7%, 30.2%, 15.1% and 89.9%, 65.1%, 22.9%, respectively. Ki-67 and CD34 expression levels in immunohistochemistry, preoperative distal metastases, maximum tumor size≥12cm and unblock/piecemeal resection were independent prognostic factors associated with OS, while Ki-67≥30% and maximum tumor size ≥12cm were found significantly associated with poor PFS (p< 0.05).

Conclusion: In a cohort of patients undergoing resection for primary RPLMS, long-term survival probabilities were not favorable remaining multimodality treatments explored in the future. Patients with tumor size larger than 12cm, concurrent with metastases and piecemeal resection more likely to have worse PFS and OS.

Table 1. Demographics, operative and pathologic details of all primary RPLMS patients.docx

Table 2 Prognostic factors associated with OS.docx