Prognostic value of circulating tumour cells in limited-stage small cell lung cancer: analysis of the concurrent ONce-daily versus twice-daily RadioTherapy (CONVERT) randomised controlled trial

Abstract

BACKGROUND: The clinical significance of circulating tumour cells (CTCs) in limited-stage small cell lung cancer (LS-SCLC) is not well defined. We report a planned exploratory analysis of the prevalence and prognostic value of CTCs in LS-SCLC patients enrolled within the phase 3 randomised CONVERT trial. PATIENTS AND METHODS: Baseline blood samples were enumerated for CTCs using CellSearch in 75 patients with LS-SCLC who were enrolled in the CONVERT trial and randomised between twice- and once-daily concurrent chemoradiation. Standard statistical methods were used for correlations of CTCs with clinical factors. Log-rank test and Cox regression analyses were applied to establish the associations of 2, 15 and 50 CTC thresholds with progression-free (PFS) and overall survival (OS). An optimal CTC count threshold for LS-SCLC was established. RESULTS: CTCs were detected in 60% (45/75) of patients (range 0-3750). CTC count thresholds of 2, 15 and 50 CTCs all significantly correlate with PFS and OS. An optimal CTC count threshold in LS-SCLC was established at 15 CTCs, defining 'favourable' and 'unfavourable' prognostic risk groups. The median OS in?<?15 vs???15 CTCs was 26.7?m vs 5.9?m (p?=?0.001). The presence of???15 CTCs at baseline independently predicted ?1?year survival in 70% and ?2?years survival in 100% of patients. CONCLUSION: We report the prognostic value of baseline CTC count in an exclusive LS-SCLC population at thresholds of 2, 15 and 50 CTCs. Specific to LS-SCLC, ?15 CTCs was associated with worse PFS and OS independent of all other factors and predicted ?2?years survival. These results may improve disease stratification in future clinical trial designs and aid clinical decision-making.