ESTRO 2023 - Abstract Book

S484

Sunday 14 May 2023

ESTRO 2023

Conclusion Use of adjuvant treatment was greatly reduced by individualised treatment in the molecular arm of the PORTEC-4a trial. In the first 6 months no significant difference in early toxicity and HRQL were found between molecular-based adjuvant treatment and standard brachytherapy, while a strong trend for better role functioning after individualised treatment was observed. OC-0602 Development of an evidence-based adjuvant treatment decision support tool for endometrial cancer L. Vermij 1 , H. Putter 2 , J. Jobsen 3 , M. Powell 4 , S. de Boer 5 , A. Leary 6 , A. Fyles 7 , P. Khaw 8 , L. Lutgens 9 , I. Jürgenliemk- Schulz 10 , M. de Jong 11 , D. Haverkort 12 , R. Nout 5 , V. Smit 1 , E. Steyerberg 2 , T. Bosse 1 , C. Creutzberg 5 , N. Horeweg 5 1 Leiden University Medical Center, Pathology, Leiden, The Netherlands; 2 Leiden University Medical Center, Medical Statistics and Bioinformatics, Leiden, The Netherlands; 3 Medisch Spectrum Twente, Radiation Oncology, Enschede, The Netherlands; 4 Barts Health NHS Trust, Clinical Oncology, London, United Kingdom; 5 Leiden University Medical Center, Radiation Oncology, Leiden, The Netherlands; 6 Gustave Roussy, Medical Oncology, Villejuif, France; 7 Princess Margaret Cancer Centre, Radiation Oncology, Toronto, Canada; 8 Peter MacCallum Cancer Centre, Radiation Oncology, Melbourne, Australia; 9 MAASTRO, Radiation Oncology, Maastricht, The Netherlands; 10 University Medical Center Utrecht, Radiation Oncology, Utrecht, The Netherlands; 11 Radiotherapy Institute Friesland, Radiation Oncology, Leeuwarden, The Netherlands; 12 Radiotherapy Group, Radiation Oncology, Arnhem, The Netherlands Purpose or Objective In 2021, the ESGO-ESTRO-ESP endometrial cancer (EC) guideline was updated with risk classification based on clinicopathological factors and the molecular classification. We aim to strengthen the evidence-base for a prognostic and therapeutic framework in women with stage I-III EC. We hereto analyzed large, completely documented cohorts to facilitate risk stratification and support decisions on adjuvant treatment. Materials and Methods Data from the PORTEC-1/-2/-3 randomized trials (n=714/427/660) and an independent prospective Dutch clinical cohort from Enschede (n=270) were pooled for analysis. Competing-risk models for vaginal, pelvic, distant, and overall recurrence and cancer-specific survival were built with established major risk factors (stage, histotype, grade, substantial lymphovascular space invasion, molecular classification) and corrected for age, and time and cohort effects. All models were developed in duplo: with and without the molecular classification. Benefits of adjuvant treatment will be estimated based on a systematic literature review and incorporated in the models within the next months. Model performance was evaluated by quantifying the time-dependent area under the receiver operating characteristic curves (AUC). Internal validation was performed according to a leave-one-cohort-out cross-validation method, where each cohort served as a validation set once for models developed without that cohort. Results In total, 2071 women with EC with a median follow-up of 10.0 years (interquartile range 6.9-12.4 years) were available for analyses (table 1). Competing risk analyses confirmed the prognostic relevance of all established clinicopathological risk factors and the EC molecular class for overall recurrence (figure 1). Performance of the prediction models including only clinicopathological factors was good (AUCs from 0.73 [95%CI 0.68-0.79] to 0.81 [95%CI 0.76-0.85]) and improved by adding the molecular classifier (AUC increased to 0.77 [95%CI 0.72-0.82] to 0.84 [95%CI 0.82-0.86]).