Prognostic Impact of Circulating Tumor Cells in Patients with Small Cell Lung Cancer

Background: Enumeration of circulating tumor cells (CTCs) may be valuable for prognostic assessment in lung cancer patients. In this study, we report the clinical significance of CTCs in small cell lung cancer (SCLC). Methods: In total, 51 consecutive patients newly diagnosed as having SCLC and starting chemotherapy or chemoradiotherapy were prospectively enrolled. Blood samples were drawn at the baseline, after chemotherapy, and at relapse. CTCs were isolated using the CellSearch System (Veridex LLC). Thresholds of 1 to 100 cells at the baseline were systematically correlated with the overall survival. The optimal cutoff was determined by comparing the Cox proportional hazard ratios (HRs). Results: Two or more CTCs were detected at baseline in 35 patients (68.6%; 95% confidence interval, 55.0-79.7). The HR signifying the difference between the unfavorable (more than or equal to threshold) and favorable (less than threshold) groups was maximal at the threshold of 8 CTCs (HR, 3.50; 95% confidence interval, 1.45-8.60). Patients with >= 8 CTCs had worse survival than those with <8 CTCs at baseline (p = 0.0014). Patients with >= 8 CTCs posttreatment or at relapse also showed worse survival than those with >= 8 CTCs (p = 0.0096 and <0.0001). Patients whose baseline and posttreatment CTC levels remained <8 tended to show better survival than those whose CTC level converted from >= 8 to <8 cells (p = 0.0288) or whose posttreatment CTC level was <8 cells (p = 0.0047). Conclusions: CTCs were highly detectable in SCLC, and higher CTC levels were strongly associated with worse survival. Consistently favorable CTC levels were associated with favorable outcomes.