[Aprospective study of detection and clinical significance of bone marrow tumor cells in small cell lung cancer].

Objective: To investigate the detection of bone marrow tumor cells in small cell lung cancer (SCLC) patients and their relationship with clinical features, treatment response and prognosis. Methods: A total of 113patients with newly diagnosed SCLC from January 2018 to October 2022 at Beijing Chest Hospital were prospectively enrolled. Before treatment, bone marrow was aspirated and separately submitted for tumor cells detection by liquid-based cytology and disseminated tumor cells (DTCs) detection by the substrction enrichment and immunostaining fluorescence in situ hybridization (SE-iFISH) platform. The correlation between the detection results of the two methods with patients' clinical features and treatment response was evaluated by Chi-square. Kaplan-Meier method was applied to create survival curves and the Cox regression model was used for multivariate analysis. Results: The positive rate of bone marrow liquid-based cytology in SCLC was 15.93% (18/113). The liver and bone metastases rates were significantly higher (55.56% vs 11.58% for liver metastasis, P ＜0.001; 77.78% vs 16.84% for bone metastasis, P ＜0.001) and thrombocytopenia was more common (16.67% vs 2.11%, P =0.033) in patients with tumor cells detected in liquid-based cytology than those without detected tumor cells. As for SE-iFISH, DTCs were detected in 92.92% of patients (105/113), the liver and bone metastasis rates were significantly higher (37.93% vs 11.90% for liver metastasis, P =0.002; 44.83% vs 20.23 % for bone metastasis, P =0.010), and the incidence of thrombocytopenia was significantly increased (13.79% vs 1.19%, P =0.020) in patients with DTCs≥111 per 3 ml than those with DTCs＜111 per 3 ml. The positive rates of bone marrow liquid-based cytology in the disease control group and the disease progression group were 12.00% (12/100) and 46.15% (6/13), respectively, and the difference was statistically significant ( P =0.002). However, the result of SE-iFISH revealed the DTCs quantities of the above two groups were 29 (8,110) and 64 (15,257) per 3 ml, and there was no statistical difference between the two groups ( P =0.329). Univariate analysis depicted that the median progression-free survival (PFS) and median overall survival (OS) of liquid-based cytology positive patients were significantly shorter than those of tumor cell negative patients (6.33 months vs 9.27 months for PFS, P =0.019; 8.03 months vs 19.50 months for OS, P =0.019, P =0.033). The median PFS and median OS in patients with DTCs≥111 per 3 ml decreased significantly than those with DTCs＜111 per 3 ml (6.83 months vs 9.50 months for PFS, P =0.004; 11.2 months vs 20.60 months for OS, P =0.019). Multivariate analysis showed that disease stage ( HR =2.806, 95% CI: 1.499-5.251, P =0.001) and DTCs quantity detected by SE-iFISH ( HR =1.841, 95% CI: 1.095-3.095, P =0.021) were independent factors of PFS, while disease stage was the independent factor of OS ( HR =2.538, 95% CI: 1.169-5.512, P =0.019). Conclusions: Both bone marrow liquid-based cytology and SE-iFISH are clinically feasible. The positive detection of liquid-based cytology or DTCs≥111 per 3 ml was correlated with distant metastasis, and DTCs≥111 per 3 ml was an independent prognostic factor of decreased PFS in SCLC.