Pre-operative tomotherapy for retroperitoneal liposarcoma: Results of a phase II multicenter study.

e22501 Background: To evaluate efficacy and feasibility of radiotherapy (RT: high-level dose 54 Gy, with 30 fractions over / 6 weeks) followed by surgery, for retroperitoneal liposarcomas. Methods: Helical tomotherapy was used for pre-operative RT. Clinical Target Volume (CTV) and main organs at risk were systematically delineated with the surgeon. Surgery was planned 4 to 8 weeks after RT. Inclusion criteria were operable, biopsy-proven, retroperitoneal liposarcomas. Toxicity was graded according to CTCAE V3.0. Overall survival (OS) was estimated using Kaplan-Meier method. Due to competing risks, we estimated the cumulative incidence of loco-regional relapse; 95% confidence intervals are reported [95%CI]. Results: Patients:From 04/2009 to 09/2013, 48 patients were included. Mean age: 62 years (y) (36 to 82). All but 1 patient were OMS ≤ 2. Histological types were 20 well differentiated (WDLS) and 28 dedifferentiated liposarcomas. Mean CTV was 2954 cc. Treatment:1 patient did not have surgery. Dosimetric constraints were respected. Monobloc exerese was systematically achieved. Surgical margins were R0 (16; 34%), R1 (28; 60%), R2 (2; 4%) or missing (1; 2%). Oncological outcomes:Median follow-up was 4.7 y. Cumulative incidence of loco-regional relapse at 3 and 5 y was 17% [8%; 29%] and 31% [16%; 47%] respectively. Estimates were 5% and 35% for dedifferentiated liposarcoma and 26% and 26% for well differentiated liposarcoma. OS at 3 and 5 y was 81% [66%; 89%]) and 78% ([63%; 88%] respectively. Toxicity: 2 months after surgery, 10 grade 3 toxicities and 1 grade 4 toxicity were reported for 6 patients; 3 patients died within 6 months after surgery, 2 of which were related to treatment. After 1 y, no further severe toxicity was observed; 5 cases of second cancers were reported: 1 myeloid leukeamia, 2 pancreatic, 2 breast carcinomas. Conclusions: This trial highlights the feasibility of preoperative 54 Gy RT. Although efficacy data (local control and OS) are encouraging, high incidence rates of acute toxicities and second cancers should be considered. Preoperative RT for WDLS remains questionable. Results from ongoing EORTC phase III Strass trial may provide further level of evidence for this approach. Clinical trial information: NCT01841047.