327. ANALYSING THE ROLE OF PET-CT IN ESOPHAGEAL CANCER: A SINGLE CENTRE COHORT STUDY

Abstract

Abstract Background While PET-CT is considered the gold standard imaging investigation in diagnosing esophageal cancer, its role in determining management is controversial. It demonstrates increased sensitivity for detection of occult M1 disease in comparison with endosonography or CT alone, however its accuracy in assessment of histopathologic response to neoadjuvant therapy is unclear. The aim of this study was to evaluate the clinical utility of PET-CT in staging, response evaluation and prognostication in esophageal squamous cell carcinoma (SCC) and adenocarcinoma (AC). Methods Patients with esophageal cancer undergoing treatment with curative intent were studied prospectively. Baseline imaging (PET1) was carried out at diagnosis. Repeat scanning (PET2) was performed at 4 weeks post-completion of neoadjuvant chemotherapy (nCT) or chemoradiation (nCRT). Pathological complete response (pCR) was defined as TRG1, ypN0. Major pathologic response was defined as TRG1–2, ypN0. Metabolic complete response (mCR) was defined as absence of abnormal FDG uptake at the primary site, nodal sites or suspected metastatic sites. The association between 18F-FDG-uptake (SUVmax) and PET-predicted nodal status, histopathologic parameters and survival were determined using univariable and multivariable regression models. Results 730 patients were studied. PET identified CT-occult M1 disease in 2.9% and synchronous neoplasms in 1.4%. The relative reduction in SUVmax was greater among patients treated with nCRT compared with nCT (P = 0.021). SUVmax correlated with pT stage among patients treated with primary surgery (P < 0.001), however 32.3% with AC and 15.8% with SCC who were predicted node negative were pN+. Post neoadjuvant therapy, PET parameters showed modest associations with mCR, but no parameter accurately predicted pCR. Among patients with mCR, 90.9% with AC post-nCT, 84.1% with AC post-nCRT and 54.8% with SCC post-nCRT had residual disease. Lower preoperative SUVmax was independently associated with improved survival in AC, but not SCC. Conclusion PET-CT identifies CT-occult M1 disease or synchronous neoplasms in 4.3% at initial staging. PET-CT poorly predicts ypN status, particularly in AC. After neoadjuvant therapy, PET-CT is poorly predictive of histopathologic response—the majority of patients with an mCR have residual disease. Nonetheless, improvements in SUVmax may reflect a greater chance of achieving major pathologic response and more favourable long-term outcomes in AC.