Incorporation of circulating tumor cells and whole-body metabolic tumor volume of (18)F-FDG PET/CT improves prediction of outcome in IIIB stage small-cell lung cancer

OBJECTIVE: We investigated the correlation between the number of circulating tumor cells (CTCs) and whole-body metabolic tumor volume (WBMTV) measured by (18)F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT). The aim was to evaluate the value of the incorporation of CTC number and WBMTV in the prognostic prediction of stage III small-cell lung cancer (SCLC). METHODS: One hundred and twenty-nine patients were enrolled in this study. All patients were treated with four cycles of a platinum-based regimen and concurrent chest irradiation, followed by prophylactic cranial irradiation. Blood samples for CTC analysis were obtained from 112 patients before the initiation of chemotherapy (as a baseline), after cycle 1 and after cycle 4. CTCs were measured using the CELLSEARCH(®) system. The patients underwent pretreatment FDG PET/CT WBMTV, which included all malignant lesions. The Spearman rank test was used to determine the correlation among CTC counts, WBMTV and disease stage. Overall survival (OS) and progression-free survival (PFS) curves were produced using the Kaplan-Meier method, and survival differences between groups were assessed by the log-rank test. RESULTS: The number of CTCs at baseline did not correlate with WBMTV before the initiation of therapy (P=0.241). The number of CTCs at baseline and the WBMTV before the initiation of therapy were independent relevant factors for PFS and OS. The subgroup analysis (Group A: CTC count >19.5 and a WBMTV >266.5 cm (3); Group B: CTC count >19.5 and a WBMTV ≤266.5 cm (3); Group C: CTC count ≤19.5 and a WBMTV >266.5 cm (3); Group D: CTC count ≤19.5 and a WBMTV ≤266.5 cm(3)) showed that the differences were statistically significant in the median PFS (Group A vs. D, P<0.001; Group Bvs. D, P=0.018; Group C vs. D, P=0.029) and in the median OS (Group A vs. D, P<0.001; Group Bvs. D, P=0.012). CONCLUSIONS: CTC number and WBMTV are related to progression and death in patients with SCLC. The incorporation of CTC number and WBMTV scans can provide a detailed prognostic prediction for SCLC.