Lymph node standardized uptake values at pre-treatment 18F-fluorodeoxyglucose positron emission tomography as a valuable prognostic factor for distant metastasis in nasopharyngeal carcinoma

Objective: The aim of the present study was to evaluate prognostic values of pre-treatment fluorine-18 fludeoxyglucose (18F-FDG) positron emission tomography (PET) parameters for predicting the distant metastasis (DM) of nasopharyngeal cancer. Methods: 73 patients diagnosed with nasopharyngeal cancer with regional lymph node (LN) involvement, who underwent pre-treatment 18F-FDG PET evaluation between January 2005 and December 2012, were retrospectively reviewed. We assessed the 18F-FDG PET parameters of the primary tumours (T–) and regional LNs (N–). For patients with bilateral retropharyngeal, bilateral neck and/or supraclavicular LN involvement, we also assessed the 18F-FDG PET parameters of the farthest LN station [N(f)–]. The following 18F-FDG PET parameters were evaluated: maximum standardized uptake value (SUVmax), mean standardized uptake value (SUVmean), peak standardized uptake value (SUVpeak), metabolic tumour volumes (MTVs) (MTV30–MTV70, which were calculated as the tumour volume with 30%, 40%, 50%, 60% and 70% of the SUVmax as the threshold, respectively) and total lesion glycolysis (TLG) (TLG30–TLG70, which were determined by the product of each MTV and the corresponding SUVmean within that MTV). Distant metastasis-free survival (DMFS) rates were estimated from the date of the start of radiotherapy to the date of DM or last follow-up by the Kaplan–Meier method. Univariate and multivariate analyses were performed to identify prognostic factors for DMFS. The median follow-up period was 53 months (range 12–110 months). Results: Most patients (95%) received concurrent chemoradiotherapy. The major failure pattern was DM (15 of all patients, 21%) and the 5-year DMFS was 79%. In univariate analysis, the T–SUVmax, T–SUVmean, T–SUVpeak, N–SUVmax, N–SUVpeak, N(f)–SUVmax and N(f)–SUVpeak were significant prognostic factors for DMFS. In multivariate analysis, the T–SUVmax, T–SUVpeak, N(f)–SUVmax and N(f)–SUVpeak were significant prognostic factors for DMFS. Of these parameters, the N(f)–SUVmax (hazard ratio = 6.524; p = 0.001) and N(f)–SUVpeak (hazard ratio = 5.399; p = 0.001) were the strongest prognostic factors for DMFS. Conclusion: In patients with nasopharyngeal cancer with LN involvement, the standardized uptake value parameter of the farthest LN station seems to be an important 18F-FDG PET parameter for predicting DM. Further studies are needed to validate its clinical significance. Advances in knowledge: We found that pre-treatment 18F-FDG PET parameters of primary tumours and regional LNs (the SUVmax and SUVpeak of the primary tumour and the farthest LN station) were significant prognostic factors for DMFS in patients with nasopharyngeal carcinoma with LN involvement.