Circulating tumor cells in small-cell lung cancer: a predictive and prognostic factor

Initial response of small-cell lung cancer (SCLC) to chemotherapy is high, and recurrences occur frequently, leading to early death. This study investigated the prognostic value of circulating tumor cells (CTCs) in patients with SCLC and whether changes in CTCs can predict response to chemotherapy. In this multicenter prospective study, blood samples for CTC analysis were obtained from 59 patients with SCLC before, after one cycle, and at the end of chemotherapy. CTCs were measured using CellSearch® systems. At baseline, lower numbers of CTCs were observed for 21 patients with limited SCLC (median = 6, range 0-220) compared with 38 patients with extensive stage (median = 63, range 0-14 040). Lack of measurable CTCs (27% of patients) was associated with prolonged survival (HR 3.4; P ≤ 0.001). CTCs decreased after one cycle of chemotherapy; this decrease was not associated with tumor response after four cycles of chemotherapy. CTC count after the first cycle of chemotherapy was the strongest predictor for overall survival (HR 5.7; 95% CI 1.7-18.9; P = 0.004). Absolute CTCs after one cycle of chemotherapy in patients with SCLC is the strongest predictor for response on chemotherapy and survival. Patients with low initial CTC numbers lived longer than those with higher CTCs.