OGC P01 Evaluating the use of FDG PET-CT for restaging patients with oesophageal adenocarcinoma treated with neoadjuvant chemotherapy

Abstract

Abstract Background 2-deoxy-2[18F]fluoro-D-glucose positron emission tomography-computed tomography (FDG-PET-CT) is routinely used for staging oesophageal cancer and has an emerging role in evaluating response to neoadjuvant chemotherapy (NACT). This study aimed to evaluate the clinical utility of FDG-PET-CT and contrast-enhanced CT (CECT) in restaging patients with oesophageal adenocarcinoma treated with NACT. The accuracy for evaluating depth of tumour invasion (ypT stage), pathological nodal disease (ypN stage) and identifying distant metastases compared with CECT was assessed. The ability of FDG-PET-CT to predict pathological response in the primary tumour (pTR) and LNs (pNR) was also evaluated. Methods Cohort study of 104 patients with locally advanced oesophageal or oesophago-gastric junctional adenocarcinoma who underwent FDG-PET-CT and CECT before and after NACT at Guy’s and St Thomas’ NHS Foundation Trust, London, UK, between 2017–2020. SUV metrics related to the primary tumour and loco-regional LNs were derived on pre- and post- treatment FDG-PET-CT. pTR and pNR were evaluated using the Mandard classification. Receiver operator characteristic analysis was performed and area under the curve (AUC) calculated to evaluate the discriminatory ability of FDG-PET-CT and CECT to predict ypT3-4 or pN positive disease. Clinicopathological characteristics were compared using the Chi-squared test. Results 91/104 patients underwent surgical resection following NACT. Four patients (3.8%) had metastatic disease identified on FDG-PET-CT only. None had metastatic disease identified on CECT only. The ability of FDG-PET-CT and CECT to predict ypT stage was comparable. However, FDG-PET-CT demonstrated better discriminatory ability (FDG-PET-CT; AUC 0.71, CECT; AUC 0.62, p=0.210). FDG-PET-CT was more accurate for ypT0-2 tumours (p=0.022), whilst CECT was superior for ypT3-4 tumours (p=0.002). The ability of both modalities to predict ypN1-3 disease was poor (FDG-PET-CT; AUC 0.55, CECT; AUC 0.53, p=1.00). Metabolic response on FDG-PET-CT was predictive of pTR (AUC 0.71, p<0.001) and pNR (AUC 0.75, p=0.010). Conclusions FDG-PET-CT after NACT identified occult metastatic disease undetected by CECT in a number of patients in this cohort, preventing futile surgery. The accuracy of FDG-PET-CT and CECT to predict ypT and ypN stage were comparable. However, CECT was more accurate for advanced tumours and FDG-PET-CT was superior for early tumours. Metabolic response on FDG-PET-CT after NACT was predictive of pathological response in both the primary tumour and LNs which may support pre-operative prognostication. These results suggest that concurrent CECT and FDG-PET-CT may be complementary for restaging and response assessment following completion of NACT prior to surgical resection.