Prognostic value of thoracic tumor staging and volume parameters in non-small cell lung cancer patients with synchronous solitary bone metastasis

Background: Non-small cell lung cancer (NSCLC) patients with synchronous solitary metastasis are a heterogeneous population. The analysis and evaluation of NSCLC patients with synchronous solitary bone metastases by cTN stage (thoracic tumor staging) and volume parameters have not yet been studied. The purpose of this study is to estimate the prognostic value of cTN stage and volume parameters obtained by fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) in NSCLC patients with synchronous solitary bone metastasis. Methods: A total of 157 NSCLC patients with synchronous solitary bone metastasis were retrospectively analyzed. Patients' cTN stage, metabolic tumor volume (MTV) parameters, and clinical data were collected. Kaplan-Meier survival analysis and a Cox regression model were performed to determine the association between each factor and overall survival (OS). Finally, time-dependent receiver operating characteristic (TDROC) curve analysis was used to assess the predictive capacity of the independent prognostic factors. Results: Kaplan-Meier survival analysis showed significant differences between subgroups in terms of cTN stage. The median OS of group I was 44 months, and the 5-year survival rate was 39.6%. In the multivariate Cox regression analysis, cTN stage, MTV of the whole body (MTVwb), and MTV of thorax (MTVtho) were significantly associated with patient OS, even after adjusting for other clinical factors. However, MTV of bone (MTVbon) was not found to be an independent prognostic factor. TDROC curve analysis showed that cTN stage, MTVwb, and MTVtho had good predictive capacity for NSCLC patients with synchronous solitary bone metastasis. Compared with cTN stage and MTVtho, MTVwb had obviously better predictive specificity and sensitivity for the 5-year survival rate [5-year area under the curve (AUC) of MTVwb =0.844 vs. cTN stage (P=0.035) vs. MTVtho (P=0.052)]. The best cutoff value of MTVwb was 33.05. Conclusions: The results of this study confirmed that cTN stage, MTVwb, and MTVtho were independent prognostic factors of NSCLC patients with synchronous solitary bone metastases. These factors can be used for risk stratification of these patients. TDROC curve analysis indicated that cTN stage, MTVtho, and MTVwb had good performance for survival prediction.