Bcl-2 expression in circulating tumor cells (CTCs) of patients with small cell lung cancer (SCLC) receiving front-line treatment.

ABSTRACT

INTRODUCTION: To investigate the presence of Bcl-2+CTCs in chemotherapy-naïve SCLC patients and their clinical relevance during front-line treatment. METHODS: Peripheral blood was obtained from 66 consecutive-patients before chemotherapy administration, after one-cycle and at relapse. CTCs were detected by CellSearch and immunofluorescence using anti-Bcl-2, anti-M30, anti-cytokeratins(CK), anti-CD45 and anti-vimentin(Vim) antibodies. RESULTS: Before treatment, CTCs were detected in 62.1% and 72.7% of patients using the CellSearch and immunofluorescence (Bcl-2+/CD45-), respectively. One-treatment cycle significantly decreased both CTCs' detection rate(p < 0.001) and their absolute number (p < 0.001). On relapse, both the number of positive-patients and the absolute number of CTC subpopulations were significantly increased, compared to post-1st cycle (CellSearch p = 0.002 and immunofluorescence p < 0.001). Immunofluorescence revealed an important CTC heterogeneity (Bcl2+/Vim+, Bcl2+/Vim-, Bcl2+/CK+, Bcl2+/CK- and Bcl2+/M30- CTCs). Moreover, 50.0% of patients without detectable CTCs by CellSearch had detectable Bcl-2+/CD45- cells. Multivariate analysis revealed a significant association between Bcl-2+/CD45-cells at baseline and PFS (HR = 4.5;p = 0.005) and OS (HR 4.3; p = 0.001). Bcl-2+/CD45-cells after one-treatment cycle were significantly associated with shorter OS (HR 13.9; p = 0.007). CONCLUSIONS: These results demonstrate an important phenotypic CTCs heterogeneity based on the co-expression of Bcl-2, CK, Vim and M30 in SCLC patients. The changes of Bcl-2+/CD45- CTCs during treatment seem to be a dynamic biomarker associated with treatment efficacy and patients' clinical outcome.