(P 460) IMPACT OF RESIDUAL TUMOR AFTER RE-EXCISION IN PATIENTS WITH PRIOR UNPLANNED RESECTION OF EXTREMITY AND TRUNK SOFT TISSUE SARCOMAS

Objective: The majority of soft tissue sarcomas (STS) arise from extremities and trunk wall. In patients with localized disease, the recommended approach consists of complete en-bloc R0 surgical resection plus radiotherapy (in high-grade lesions, G2-3) after multidisciplinary tumor board evaluation. In patients with microscopically positive margin resection (R1), the probability of residual disease in tumor bed has led to evaluate the utility of re-resection. The aim of this study was to evaluate the impact of residual tumor in patients who underwent re-excision after unplanned R1 resection.

Methods: We analyzed retrospectively from a prospectively maintained database all patients (≥18yo) with extremity and trunk STSs treated in two referral centers in Argentina who underwent re-excision after prior R1 resection from January/2000 to December/2020. Demographic data and tumor characteristics were evaluated (location, size and neo/adjuvant treatment delivered). In order to compare oncologic results, the series was divided in two groups: G1 (residual tumor present in re-excision specimen) and G2 (no residual tumor). We evaluated overall survival (OS, death defined as event) and local recurrence-free survival (LRFS, recurrence defined as event). Survival was defined from time of re-excision to event detection.

Results: We identified 102 patients; median age 46(IQR, 31-59) years and 52(51%) patients were females. The tumor was located in trunk-wall in 30 (29.5%) patients and limbs in 70(70.5%) patients. Data on grade was available for 73 lesions and 63% (46/73) were high-grade. In 24 (23.5%) patients, residual tumor was detected after re-excision (Group 1) and the remaining 78 correspond to Group 2. After re-excision recurrence was observed in 10(41.6%) of 24 patients in Group 1, and 18 (23%) of 78 patients in Group 2 (p=0.12). Noteworthy 71% (20/28) of LRs happened in extremity locations and 65% (13/20) did not have RT. The 2-year and 5-year recurrence-free survival was 76% and 38% for Group 1 and 78% and 75% for Group 2 (p=0.08, Figure 1), respectively. The 5-year overall survival was 94% in Group 1 and 92% in Group 2 (p=0.58, Figure 2).

Conclusion: In our series, the presence of residual tumor after re-excision was observed in 23.5% of patients with prior unplanned R1 resection. We did not find a negative impact in terms of LRFS and OS when compared with patients without residual tumor. Nevertheless, the higher rate of recurrence in patients with residual tumor (G1) could lead to a potential more extensive and eventually radical resection, mainly in patients with extremity sarcomas, in case of late detection during follow up. The size of our series and the retrospective nature of this study avoid establishing a firm recommendation.