RA07.06: BASELINE FDG-PET/CT PARAMETERS AS PREDICTOR FOR RESIDUAL TUMOUR AFTER NEOADJUVANT CHEMORADIOTHERAPY IN OESOPHAGEAL CANCER PATIENTS

Abstract

Abstract Background An optimal model for predicting pathologic response after neoadjuvant chemoradiotherapy (nCRT) in oesophageal cancer has not been defined yet. FDG-PET/CT is frequently used in response assessments. The aim of this side study of the preSANO trial (NL41732.078.13) was to investigate if the FDG-PET parameters SUVmax, total lesion glycolysis (TLG) and metabolic tumour volume (MTV) were predictive for residual tumour in the resected specimen of oesophageal cancer patients treated with nCRT. Methods Patients underwent FDG-PET/CT at baseline according to the European Association of Nuclear Medicine guidelines 1.0 (2.3MBq/kg F-18-FDG; scanning 60 ± 5min.). All parameters were corrected for lean body mass. MTV was defined as the volume within a 41% of SULmax ( = SUV/lean body mass) isocontour threshold at tumour and lymph nodes. TLG was calculated as SULmean x MTV. Logarithmic transformation was performed because of non-normal distribution of TLG and MTV. Baseline PET parameters were compared to tumour regression grade in the resection specimen (TRG3–4 = > 10% residual tumour vs. TRG1 = complete response). Peroperatively irresectable tumours were recoded as TRG4. Analyses were performed using an independent-samples T-test. Results From a total of 207 patients who underwent FDG-PET/CT before nCRT, 197 were included for analysis (5 were non-FDG avid, 5 had incomplete data). Histological type of tumour: adenocarcinoma (AC) n = 154, squamous cell carcinoma (SCC) n = 42, and one adenosquamous carcinoma. Thirty-seven patients (19%) had TRG1 and 41 patients (21%) had TRG3–4. In complete responders (TRG1), SULmax, TLG and MTV (mean ± SD) were 9.6 ± 5.8, 85.3 ± 85.5 and 13.0 ± 9.9, respectively. In patients with TRG3–4, SULmax, TLG and MTV were 9.4 ± 5.4145.8 ± 164.6 and 21.9 ± 16.2, respectively. SULmax was not significantly different between both groups (P = 0.8), but log(TLG) and log(MTV) (P = 0.008 and P = 0.001) were. In adenocarcinomas, log(TLG) did not differ between groups (P = 0.1). Conclusion Initial FDG tumour mass, expressed as MTV, (rather than SULmax) is the most contributing factor in predicting residual disease after nCRT in both SCC and AC. The effect is stronger in SCC. Therefore, baseline FDG tumour mass should be included in a prediction model, besides other clinical and tumour parameters. Disclosure All authors have declared no conflicts of interest.