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Metabolic tumour volume (MTV) measured on fluorodeoxyglucose F18 (FDG) positron emission tomography coupled with computed tomography (PET/CT) is a prognostic factor of advanced non-small cell lung cancer (NSCLC) treated by first-line immunotherapy. However, these tumours are often necrotic and the necrosis, which is hypometabolic in PET FDG, is not included in the MTV. The aim of this study was to evaluate the prognostic value of total tumour volume (TTV), adding necrotic tumour volume (NTV) to metabolic tumour volume (MTV).We retrospectively included 65 patients with NSCLC treated with pembrolizumab as monotherapy. All patients had a pretreatment FDG PET/CT. PET/CT measured parameters were MTV, NTV and TTV. Clinical, biological and tumour parameters were also retrieved. Receiver operator characteristics (ROC) analysis was performed and overall survival at 1 year was studied using Kaplan-Meier and uni/multivariate Cox analysis.In the ROC analysis, MTV, NTV, TTV, age at diagnosis, polynuclear blood neutrophil, derived neutrophil/leukocyte ratio (dNLR), and haemoglobin had an area under the curve (AUC) significantly higher than 0.5. In Kaplan-Meier analysis, prognosis was worse for patients with high MTV (p = 0.02), high TTV (p = 0.003), high NTV (p = 0.014), low haemoglobin (p 0.001), older people (p = 0.002), neutrophil polynucleosis (p 0.001) and dNLR (p = 0.022). All these parameters, except age and neutrophil polynucleosis, were significant prognostic factors in univariate Cox analysis (p 0.05). In a stepwise multivariate Cox analysis focused on PET parameters, the only significant parameter was TTV (HR = 3.66, p = 0.002) and in a stepwise multivariate Cox analysis exploring all the parameters, a model combining TTV, performance status and brain metastasis was found (p = 0.002).TTV and NTV measured on pretreatment FDG PET/CT are significant prognosis factor for stage III-IV NSCLC treated by pembrolizumab and TTV could have a higher prognostic value than MTV.