Analysis of the prognostic role and biological characteristics of circulating tumor cell-associated white blood cell clusters in non-small cell lung cancer

Background: Recently, circulating tumor-cell-associated white blood cell (CTC-WBC) clusters have been reported to have prognostic value in some cancers. The prognostic role of CTC-WBC clusters in lung cancer has not yet been elucidated. Very little information is available about the biological characteristics of CTC-WBC clusters.

Methods: A total of 82 patients with non-small cell lung cancer (NSCLC) were included in this study, and 61 patients with advanced-stage disease were closely followed-up. All patients had blood drawn prior to treatment. Subtraction enrichment and immunostaining-fluorescence in situ hybridization (SE-iFISH) platform was used to isolate and identify CTCs and CTC-WBC clusters. Kaplan-Meier survival analysis and Cox regression analysis were applied to assess patient progression-free survival (PFS). Further, qualitative and quantitative analyses the size and ploidy characteristics of CTC-WBC clusters.

Results: Firstly, CTC-WBC clusters appeared more in the advanced (stage III and IV) stage (P=0.043) than in the early stage. Furthermore, the multivariable analysis (Cox proportional hazards model) revealed that the high-CTC (≥7/6 mL) group and CTC-WBC clusters (≥1/6 mL) positive group both had significantly worse PFS, with a hazard ratio (HR) of 2.89 [95% confidence interval (CI): 1.36-6.17, P=0.006] and 2.18 (95% CI: 1.07-4.43, P=0.031), respectively. In the conjoint analysis, compared to patients with <7 CTCs/6 mL without CTC-WBC clusters, patients with ≥7 CTCs/6 mL with CTC-WBC clusters had the highest risk of progression (HR =7.13, 95% CI: 2.51-20.23, P<0.001). In addition, the presence of ≥3-cell CTC-WBC clusters in patients may indicate a shorter PFS (P<0.05) and a higher risk of progression (HR =2.90, 95% CI: 1.06-7.89, P=0.037). Furthermore, compared with the characteristics of the total CTCs, almost all of the CTCs that could recruit WBCs were large cells (≥5 µm) and exhibited polyploidy (≥ tetraploid) (both P<0.01).

Conclusions: The presence of CTC-WBC clusters was an independent prognostic factor for advanced NSCLC. The joint analysis of CTCs and CTC-WBC clusters could provide additional prognostic value to the enumeration of CTCs alone. Besides, most of the CTCs in CTC-WBC clusters were large polyploid cells.