(P 314) AN INTERNATIONAL, MULTI-CENTRE STUDY OF SURGICAL MARGINS IN INTERMEDIATE TO HIGH GRADE SARCOMA

Objective: Surgical resection with a negative margin typically forms the cornerstone of curative management in sarcoma, with positive margins associated with increased local recurrence (LR). Most margins studies include all sarcoma subtypes as a single entity and fail to appreciate the diverse characteristics of various histological subtypes. This study aims to compare the influence of margins on outcome in different histological subtypes and define a ‘close’ pathological margin.

Methods: Patients treated for intermediate to high grade sarcomas at 5 centres from 3 countries between 01/01/2010 and 31/12/2015 were included. Visceral, retroperitoneal and intracranial tumours were excluded. Statistical analysis was performed using R Studio.

Results: 1510 patients were suitable for inclusion. Overall, the positive margin rate was 17.6% and the 5-year local recurrence (LR) was 12.6%; positive margin and LR rates varied greatly between subtypes, with no correlation. Overall, positive margins were associated with increased LR (HR=3.59, p< 0.0001) and decreased overall survival (OS) (HR=1.495, p< 0.001) as expected. When analysing histological subtypes independently, only myxofibrosarcoma, undifferentiated pleomorphic sarcoma (UPS), angiosarcoma, and spindle cell sarcoma (SCS) had increased LR with positive margins (p=0.002/ < 0.0001/0.0067/0.0091 respectively). In myxofibrosarcoma, UPS and SCS, a closest margin of 10mm reduced the LR risk to 5% (p < 0.05). In angiosarcoma, a closest margin 30mm reduced the LR risk to 10% (p=0.021). Surprisingly, positive margins were only associated with decreased OS in angiosarcoma and myxoid liposarcoma (p=0.042/0.0059 respectively). A closest margin of >2mm in myxoid liposarcoma significantly improved OS (p=0.022).

Conclusion: This study is the first to truly demonstrate the varying importance of surgical margins in different histological subtypes. Dedifferentiated liposarcoma, leiomyosarcoma and synovial sarcoma have low margin risk (negative sufficient). Myxoid liposarcoma is medium risk (2mm or more recommended). Myxofibrosarcoma, UPS and SCS are high risk (10mm or more). Angiosarcoma is very high risk (30mm/entire field).