Prognostic value of metabolic tumor burden on ¹⁸F-FDG PET in nonsurgical patients with non-small cell lung cancer

The objective of this study was to assess the prognostic value of metabolic tumor burden on 2-deoxy-2-[¹⁸F]fluoro-D-glucose (¹⁸F-FDG) positron emission tomography (PET)/CT measured with metabolic tumor volume (MTV) and total lesion glycolysis (TLG), independent of Union Internationale Contra la Cancrum (UICC)/American Joint Committee on Cancer (AJCC) tumor, node, and metastasis (TNM) stage, in comparison with that of standardized uptake value (SUV) in nonsurgical patients with non-small cell lung cancer (NSCLC).

This study retrospectively reviewed 169 consecutive nonsurgical patients (78 men, 91 women, median age of 68 years) with newly diagnosed NSCLC who had pretreatment ¹⁸F-FDG PET/CT scans. The ¹⁸F-FDG PET/CT scans were performed in accordance with National Cancer Institute guidelines. The MTV of whole-body tumor (MTV_WB), of primary tumor (MTV_T), of nodal metastases (MTV_N), and of distant metastases (MTV_M); the TLG of whole-body tumor (TLG_WB), of primary tumor (TLG_T), of nodal metastases (TLG_N), and of distant metastases (TLG_M); the SUV_max of whole-body tumor (SUV_maxWB), of primary tumor (SUV_maxT), of nodal metastases (SUV_maxN), and of distant metastases (SUV_maxM) as well as the SUV_mean of whole-body tumor (SUV_meanWB), of primary tumor (SUV_meanT), of nodal metastases (SUV_meanN), and of distant metastases (SUV_meanM) were measured with the PETedge tool on a MIMvista workstation with manual adjustment. The median follow-up among survivors was 35 months from the PET/CT (range 2–82 months). Statistical methods included Kaplan-Meier curves, Cox regression, and C-statistics.

There were a total of 139 deaths during follow-up. Median overall survival (OS) was 10.9 months [95% confidence interval (CI) 9.0–13.2 months]. The MTV was statistically associated with OS. The hazard ratios (HR) for 1 unit increase of ln(MTV_WB), √(MTV_T), √(MTV_N), and √(MTV_M) before/after adjusting for stage were: 1.47/1.43 (p < 0.001/<0.001), 1.06/1.05 (p < 0.001/<0.001), 1.11/1.10 (p < 0.001/<0.001), and 1.04/1.03 (p = 0.007/0.043), respectively. TLG had statistically significant associations with OS with the HRs for 1 unit increase in ln(TLG_WB), √(TLG_T), √(TLG_N), and √(TLG_M) before/after adjusting for stage being 1.36/1.33 (p < 0.001/<0.001), 1.02/1.02 (p = 0.001/0.002), 1.05/1.04 (p < 0.001/<0.001), and 1.02/1.02 (p = 0.003/0.024), respectively. The ln(SUV_maxWB) and √(SUV_maxN) were statistically associated with OS with the corresponding HRs for a 1 unit increase before/after adjusting for stage being 1.46/1.43 (p = 0.013/0.024) and 1.22/1.16 (p = 0.002/0.040). The √(SUV_meanN) was statistically associated with OS before and after adjusting for stage with HRs for a 1 unit increase of 1.32 (p < 0.001) and 1.24 (p = 0.015), respectively. The √(SUV_meanM) and √(SUV_maxM) were statistically associated with OS before adjusting for stage with HRs for a 1 unit increase of 1.26 (p = 0.017) and 1.18 (p = 0.007), respectively, but not after adjusting for stage (p = 0.127 and 0.056). There was no statistically significant association between OS and √(SUV_maxT), ln(SUV_meanWB), or √(SUV_meanT). There was low interobserver variability among three radiologists with intraclass correlation coefficients (ICC) greater than 0.94 for SUV_maxWB, ln(MTV_WB), and ln(TLG_WB). Interobserver variability was higher for SUV_meanWB with an ICC of 0.806.

Baseline metabolic tumor burdens at the level of whole-body tumor, primary tumor, nodal metastasis, and distant metastasis as measured with MTV and TLG on FDG PET are prognostic measures independent of clinical stage with low inter-observer variability and may be used to further stratify nonsurgical patients with NSCLC. This study also suggests MTV and TLG are better prognostic measures than SUV_max and SUV_mean. These results will need to be validated in larger cohorts in a prospective study.