[Investigation of Methods and Influencing Factors to Increase the Positive Rate of 
Cytological Pathology of Cerebrospinal Fluid from Lung Cancer Leptomeningeal Metastases].

BACKGROUND: In advanced non-small cell lung cancer (NSCLC), leptomeningeal metastases (LM) is a common consequence with rapid progression and a poor prognosis. LM affects roughly 3% to 5% of NSCLC patients, and it affects as many as 9.4% of individuals with epidermal growth factor receptor (EGFR) mutations. Cerebrospinal fluid cytology is the gold standard for diagnosing LM, while conventional cytopathology has a positive detection rate of less than 50%, resulting in a delay in diagnosis and treatment of LM. The fixation treatment of cerebrospinal fluid samples has a significant impact on the positive cytology detection rate, and how to improve the positive cytopathology detection rate of cerebrospinal fluid is a hot topic in clinical research.

METHODS: From June 2019 to November 2021, 105 cases diagnosed with LM based on clinical symptoms and positive imaging were collected and retrospectively evaluated in the second ward of the Department of Oncology of The Second Affiliated Hospital of Harbin Medical University. The effect of different fixation methods on the positive rate of cerebrospinal fluid cytopathology was investigated, and specimens of cerebrospinal fluid were collected and sent for examination using different delivery methods, including the application of the TIB cell preservation solution kit (experimental group) and the routine application of sterile plastic tubes in lumbar puncture bags (control group). Biochemical assays (glucose and total protein) were performed on the cerebrospinal fluid fluid, and Logistic regression analysis and receiver operating characteristic (ROC) curve were used to evaluate the supplementary diagnostic value for LM patients with lung cancer. The relevance of chemical indexes in the assessment of therapeutic efficacy was examined, and biochemical (glucose, total protein) indices and cytological changes in cerebrospinal fluid fluid after pemetrexed intrathecal injection therapy were dynamically monitored.

RESULTS: In the control group, 24 (45.28%) patients were positive for the first time, while 42 (80.77%) patients were positive for the first time and 10 (19.23%) patients were negative for the first time in the experimental group. Significant differences existed between the two groups (P<0.001). The results of Logistic regression analysis of patients with the first cerebrospinal fluid biochemical test showed that the risk of positive cerebrospinal fluid biochemical pathology with less than 2.5 mmol/L was 2.456 times greater than 2.5 mmol/L of cerebrospinal fluid glucose (OR=2.456, P<0.05), and total cerebrospinal fluid biochemical protein greater than 430 mg/L was 2.647 times less than 430 mg/L (OR=2.647, P>0.05). The ROC curve showed glucose sensitivity of 76.9% in cerebrospinal fluid, the specificity of 54.5%, Youden index of 0.315 and area under the curve (AUC) of 0.620, total protein sensitivity in cerebrospinal fluid of 44.4%, 90.6%, Youden index of 0.350 and AUC of 0.671. After 2 cycles of pemetrexed intrathecal treatment with complete cerebrospinal fluid cytology and cerebrospinal fluid biochemical (glucose, total protein) tests in 73 and 50 patients, respectively, the rate of cerebrospinal fluid cytology turning negative was gradually increased. Cerebrospinal fluid glucose levels increased after 2 cycles of treatment compared with the first time, with a statistically significant difference (P<0.001).

CONCLUSIONS: The use of a cell preservation solution kit to immediately fix cerebrospinal fluid samples following isolation in patients with clinical symptoms and positive imaging greatly enhances the rate of positive cerebrospinal fluid cytology detection. The effect of treatment can be assessed and predicted by continuous dynamic monitoring of cerebrospinal fluid biochemistry and cytology.