Abstract Book

ESTRO 37

S411

therapy. Preferences regarding these new treatment strategies are yet unknown. In this study we determined preferences and utility scores for surgical and organ- sparing rectal cancer treatment approaches in patients with a history of rectal cancer and healthy volunteers. Material and Methods This is a cross-sectional study conducted at the Radiation-Oncology Department of a tertiary center. Fifty-seven patients with a history of rectal cancer and 38 volunteers were included. Participants assessed six hypothetical treatment-outcome scenarios for intermediate and high risk rectal cancer including short- course radiotherapy (SCRT) followed by low anterior resection (LAR) or abdominoperineal resection (APR) and chemoradiation followed by LAR, APR, local excision or a non-operative wait-and-see approach. Each scenario explained treatment details, hospital stay, risk of complications, common symptoms, functional outcomes, follow-up schedule and the five-year local recurrence risk. Hierarchy in preferences between scenarios was assessed using ranking. Utilities were estimated with visual analogue scale (VAS) and time trade-off (TTO). Results Of all 95 participants, 51% ranked an organ-sparing approach (local excision or wait-and-see) as first preferred treatment option. Wait-and-see was most often the highest preferred treatment scenario in patients and in volunteers (36% and 50% respectively) (Figure 1). Meanwhile, a substantial proportion ranked wait-and-see as their lowest preference (38% in patients and 35% in volunteers). SCRT followed by LAR was the most preferred surgical approach (ranked highest by 24% of the participants), and chemoradiation followed by APR the least preferred (lowest ranked by 38% of the participants). VAS- and TTO scores differed significantly between all scenarios. Wait-and-see received a significantly higher VAS score than the two scenarios including APR and the scenario including chemoradiation with LAR, and a similar VAS score as the scenarios including local excision and SCRT with LAR (Table 1) Figure 1. First and last treatment preference stratified by patients with a history of rectal cancer and healthy volunteers.

PO-0793 Metformin with neoadjuvant chemoradiotherapy in the management of locally advanced rectal cancer T. Leroy 1 , E. Bogart 2 , E. Decoupigny 3 , J.B. Prevost 4 , N. Blanchard 5 , L. Gilbeau 6 , A. Henni 7 , D. Carlier 8 , O. Olsyk 9 , M. Tokarski 10 , X. Mirabel 1 1 Centre Oscar Lambret, Radiotherapy, Lille, France 2 Centre Oscar Lambret, Statistics, Lille, France 3 Centre Oscar Lambret, Clinical research Unit, Lille, France 4 Centre Pierre Curie, Radiotherapy, Beuvry, France 5 Clinique des Dentellières, Radiotherapy, Valenciennes, France 6 Centre Gray, Radiotherapy, Maubeuge, France 7 Centre Marie Curie, Radiotherapy, Arras, France 8 Centre Leonard de Vinci, Radiotherapy, Dechy, France 9 Centre Galilée, Radiotherapy, Lille, France 10 Centre Hospitalier, Radiotherapy, Lens, France Purpose or Objective Metformin has been shown to have anti-neoplastic activity in colorectal cancer an to synergize with chemoradiotherapy. The objective of this study was to assess prospectively the efficacy of the safety of metformin in addition to neoadjuvant chemoradiotherapy in the management of locally advanced rectal cancer Material and Methods We conducted a one-arm multicentric phase II trial in which metformin was added to neoadjuvant chemoradiotherapy. ( 50 Gy in 25 fractions with concurrent capecitabin 800mg/m2 bid 5 days /7). Metformin was given daily 850 mg tid during chemoradiotherapy until 48 hours before surgery. Surgery was planned between 6 and 8 weeks after the end of chemoradiotherapy. Main endpoint was pathological complete response rate (pcr). Secondary endpoints were downstaging and toxicities rates. Downstaging was defined as the rate of ypT0-2N0 tumors. Patients could be included if they had a T3 or T4 tumor of the middle or lower rectum. Diabetics patients were excluded of this study. Results 60 patients were included between June 2015 and November 2016 from 8 centers. 57 were evaluable for pCR and 58 for safety. We observed 9 pCR (15,8%) which was not statistically different from the theoretical rate (p=0,67). The downstaging rate was 64% IC95% (50-77%) and higher than those previously reported. Nodal downstaging was 79%. Metformin was well tolerated. We observed 15 grade 3 or higher treatment related toxicities which were mainly lymphopenia (n=6) and diarrhea (n=4) Conclusion Despite showing no gain in terms of pCR, metformin shows interesting activity signals in rectal cancer with a good tolerance. PO-0794 Patient preferences for surgical and organ- sparing treatment approaches for rectal cancer A.M. Couwenberg 1 , M.P.W. Intven 1 , J.P.M. Burbach 2 , M.J. Emaus 3 , W.M.U. Van Grevenstein 4 , H.M. Verkooijen 3 1 UMC Utrecht, Radiotherapy, Utrecht, The Netherlands 2 UMC Groningen, Surgery, Utrecht, The Netherlands 3 UMC Utrecht, Imaging Division, Utrecht, The Netherlands 4 UMC Utrecht, Surgery, Utrecht, The Netherlands Purpose or Objective Organ-sparing approaches, including wait-and-see and local excision, are increasingly being offered to rectal cancer patients with a good response to neoadjuvant