P-OGC24 Comparison of the histopathological regression after neoadjuvant FLOT versus ECX in resectable gastroesophageal adenocarcinoma

Background Neoadjuvant chemotherapy is a key component in the treatment of resectable oesophagogastric cancer (OGC). Histopathological tumour regression is associated with a prognostic benefit in OGC. There is increased usage of the FLOT regimen as part of neoadjuvant chemotherapy (NAC) for these tumours. The initial phase 2 trial demonstrated complete pathological response (pCR) in 15% for FLOT versus 6% for ECX but there is no data outside a trial setting. The aim of this study was to evaluate the differences in pCR and the extent of downstaging between patients receiving FLOT versus ECX in the neoadjuvant setting.  Methods Consecutive patients treated for OGC in a single, high-volume UK centre between 2018 and 2021 were identified from a contemporaneously maintained database. Patients underwent 3 cycles of ECX or 4 cycles of FLOT as part of NAC. Histopathological tumour regression was assessed by the Mandard classification. A comparison of T- and N stage migration between FLOT and ECX was performed. Major pCR was defined as TRG 1-2 based on the Mandard classification. Results The study included 162 patients. 6/84 (7.1%) patients receiving ECX and 5/78 (6.4%) patients receiving FLOT achieved a pCR (p = 0.853). 11/84 (13.1%) patients in the ECX group and 12/78 (15.4%) patients in the FLOT group achieved a major pCR (p = 0.677). With regards to stage migration by T-stage, 36 (42.9%) patients were downstaged and 6 patients (7.1%) were upstaged with ECX. Amongst FLOT patients, 42 (53.8%) were downstaged and 8 (10.3%) upstaged (p = 0.189). When comparing N-stage, 29 (34.5%) patients achieved downstaging and 28 (33.3%) were upstaged with ECX. 30 (38.5%) patients were downstaged and 20 (25.6%) were upstaged with FLOT (0.563).  Conclusions There was no significant difference in pCR and stage migration rates between patients receiving neoadjuvant ECX and FLOT. pCR rates were lower than previously reported, and it is unclear if the difference in prognosis will translate comparable outcomes between patients receiving ECX versus FLOT.