Risk-stratifying capacity of PET/CT metabolic tumor volume in stage IIIA non-small cell lung cancer.

Objectives: Stage IIIA non-small cell lung cancer (NSCLC) is heterogeneous in tumor burden, and its treatment is variable. Whole-body metabolic tumor volume (MTV) has been shown to be an independent prognostic index for overall survival (OS). However, the potential of MTV to risk-stratify stage IIIA NSCLC has previously been unknown. If we can identify subgroups within the stage exhibiting significant OS differences using MTV, MTV may lead to adjustments in patients' risk profile evaluations and may, therefore, influence clinical decision making regarding treatment. We estimated the risk-stratifying capacity of MTV in stage IIIA by comparing OS of stratified stage IIIA with stage IIB and IIIB NSCLC.

Methods: We performed a retrospective review of 330 patients with clinical stage IIB, IIIA, and IIIB NSCLC diagnosed between 2004 and 2014. The patients' clinical TNM stage, initial MTV, and long-term survival data were collected. Patients with TNM stage IIIA disease were stratified by MTV. The optimal MTV cutoff value for stage IIIA patients was calculated using sequential log-rank tests. Univariate and multivariate cox regression analyses and Kaplan-Meier OS analysis with log-rank tests were performed.

Results: The optimal MTV cut-point was 29.2 mL for the risk-stratification of stage IIIA. We identified statistically significant differences in OS between stage IIB and IIIA patients (p < 0.01), between IIIA and IIIB patients (p < 0.01), and between the stage IIIA patients with low MTV (below 29.2 mL) and the stage IIIA patients with high MTV (above 29.2 mL) (p < 0.01). There was no OS difference between the low MTV stage IIIA and the cohort of stage IIB patients (p = 0.485), or between the high MTV stage IIIA patients and the cohort of stage IIIB patients (p = 0.459). Similar risk-stratification capacity of MTV was observed in a large range of cutoff values from 15 to 55 mL in stage IIIA patients.

Conclusions: Using MTV cutoff points ranging from 15 to 55 mL with an optimal value of 29.2 mL, stage IIIA NSCLC may be effectively stratified into subgroups with no significant survival difference from stages IIB or IIIB NSCLC. This may result in more accurate survival estimation and more appropriate risk adapted treatment selection in stage IIIA NSCLC.