ESTRO 2023 - Abstract Book

S1126

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ESTRO 2023

on 6-month interval imaging. However, these patients need to be under close surveillance as they are at highest risk of disease progression.

PO-1397 Can rectal cancer be cured without surgery? FOREST protocol an alternative to TNT

M.D. De Las Peñas Cabrera 1 , S. Payano Hernandez 1 , P.M. Samper Ots 1 , E.J. Amaya Escobar 2 , J. Zapatero Ortuño 3 , C. Garcia Torres 2 , B. Martinez Amores-Martinez 4 , J. Silva Ruiz 4 , D. Alias Jimenez 5 1 University Hospital Rey Juan Carlos, Radiation Oncology, MADRID, Spain; 2 University Hospital Rey Juan Carlos, Radiation Oncologist, MADRID, Spain; 3 University Hospital Rey Juan Carlos, Radition Oncologist, MADRID, Spain; 4 University Hospital Rey Juan Carlos, Medical Oncology, MADRID, Spain; 5 University Hospital Rey Juan Carlos, General Digestive Surgery, MADRID, Spain Purpose or Objective The FOREST protocol (FOuR-Evaluation-STage) is a total neoadjuvant treatment strategy, with “EARLY” ASSESSMENT of response (MRI between 4th and 6th week after CTRT completion); with physical, nutritional and psychological "MULTIMODAL" PREHABILITATION during treatment and a model of SHARED DECISIONS with the patient. The objective of the present study is to evaluate the cure rate with complete response without the need for surgery using this treatment scheme. Materials and Methods Design: open prospective observational study. A total of 26 patients (Nov 2020-Aug 2022) met the inclusion criteria. A treatment scheme with chemoradiotherapy with capecitabine as radiosensitizer and TNT with mFOLFOX Vs. XELOX scheme was used. Demographic data, types of treatment, and clinical course and response data were recorded. We defined a composite variable called success as those cases that did not require surgery and that were free of disease. Chi squared was used for comparisons. Statistical significance was set at 95% level (p < 0,05) Results The descriptive analysis is shown in TABLE 1. Most of patients were male (73.1%), with a mean age of 62.74 years. In the vast majority (96.2%) the histology was adenocarcinoma. The main locations were in either the lower (42.3%) and in the middle (46.2%) rectum. More than half (53.8%) were stage IIIC having most of them (65.4%) free circumferential margin. The treatments are described in TABLE 2. Only 4 patients (15.4%) received a short regimen (25 Gy). Most of them received 6 CT cycles. The mean follow-up from the end of treatment was 30.86 weeks (+/- 19.98%) (0-59). From the 26 patients, 20 (76.92%) had finished the treatment and 16 of them had MRI, rectoscopy and biopsy. From these, 14 lived free of disease, 9 without needing surgery (56.3%) and 5 after surgery (31.25%). The remaining 2 lived with rectal surgery and had been operated (12.5%). Success was achieved in 9 cases (9/16; 56.3%). The only variable that significantly influenced the success rate was the presence or absence of free margins. In those cases, with free margins, success was achieved in 72.72% of cases (8/11) compared to only 20% in those with an affected margin (1/5) (p = 0.04). Another variable associated with therapeutic success, although of borderline significance, was the dose of radiotherapy, achieving success in only 33.3% (1/3) of the patients with short regimen. Gender, age, tumor location and clinical stage did not influence the rate of therapeutic success.