378 Mind the Gap: Radiological-Pathological Discrepancies After FLOT in Gastric Cancer

Abstract Aim Perioperative chemotherapy is the standard of care for resectable gastric cancer in the United Kingdom, with CT imaging routinely used before and after neoadjuvant chemotherapy (NAC) to assess tumour response. This study aimed to evaluate concordance between initial radiological staging (rTNM), post-NAC radiological re-staging (yrTNM), and final pathological staging (ypTNM). Method A retrospective cohort study was conducted from January 2018 to May 2025, including adult patients with histologically confirmed gastric adenocarcinoma treated with neoadjuvant FLOT chemotherapy with curative intent. Concordance between rTNM, yrTNM, and ypTNM was assessed. Agreement between yrTNM and Mandard tumour regression grade was also analysed to evaluate the accuracy of radiological response assessment. Results A total of 123 patients were included (mean age 64 years, 69% male). AJCC stage at diagnosis was stage I - 15%, stage II - 44%, stage III - 40%, stage IV - 1%. Concordance between rTNM and ypTNM was slight (κ = 0.141, p = 0.016), as was agreement between yrTNM and ypTNM (κ = 0.130, p = 0.028). Post-NAC CT underestimated disease burden in 28 patients; 7 (5.7%) had unresectable disease at surgery, and 21 (17.1%) showed progression on final pathology. No significant association was found between yrTNM and Mandard grade (χ²(1) = 2.326, p = 0.127), suggesting radiological downstaging is not a reliable predictor of histological response. Conclusions Post-NAC CT re-staging demonstrated limited accuracy in assessing tumour response. These findings highlight the need to refine imaging protocols or explore alternative staging strategies to improve surgical decision-making following neoadjuvant therapy.