wetenschapsdag 2023 | 51 Sessie 1d: Een Goede Fundering Voor de Chirurgische Lering x4 Auteurs B. M. Geubels, A. van den Esschert, S.J.D. Temmink, P.J. Nilsson, K.C.M.J. Peeters, G.L. Beets, B.A. Grotenhuis (on behalf of the Dutch and International Watch-and-Wait consortium) Abstract titel Outcomes of Watch-and-Wait after short-course radiotherapy in an international multicentre Watch-and-Wait registry Background Watch-and-Wait (W&W) is an organ preservation treatment for rectal cancer patients with a clinical complete response (cCR) after chemoradiation (CRT). However, since most W&W evidence is based on CRT, standard practice following short-course radiotherapy (SCRT) involves (delayed) TME-surgery, particularly without response evaluation. This study aims to evaluate whether cCR following SCRT yields comparable outcomes to CRT in a large international W&W cohort. Methods Patients following W&W after SCRT between 2009 and 2022 were included from the International W&W registry. Response evaluation, oncological outcome, and organ preservation were assessed. Results 161 rectal cancer patients following W&W after SCRT were included: 40% were cT1-2 and 60% were cT3-4 at baseline, and 59% had cN+ disease. Median follow-up was 28 months. First response assessment took place at median 10 weeks after end of radiotherapy. At first response assessment, 61% of the patients had cCR and 39% near-complete response (nCR). Of the patients with nCR, 60% achieved cCR at reassessment (median 22 weeks after end of radiotherapy) and 5% underwent TME-surgery for persistent nCR. Of the remaining nCR-patients, 32% underwent local excision and 2% contact x-ray brachytherapie in order to achieve cCR. Overall, local regrowth occurred in 22/162 cases (14%), all located in the bowel wall and all diagnosed within the first two years of W&W follow-up. There were no significant differences between patients with initial cCR or nCR. Distant metastases occurred in 3% of cases. The 2- and 5-year TME-free disease-free survival was 81.4% and 71.8%. Finally, 86% of the patients following W&W after SCRT successfully underwent organ preservation. Conclusion A clinical (near-)complete response after SCRT yields favorable outcomes in terms of organ preservation and W&W appears to be oncologically safe, with comparable results to CRT. This study emphasizes the importance of response evaluation after SCRT: in case of clinical (near-)complete response, W&W can be considered
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