In this study, we applied CSF mNGS-CNVs analysis and cytological examinations in a cohort of 51 patients diagnosed with leptomeningeal malignancy and inflammatory diseases. The main findings are summarized as follows. Firstly, we established a well-designed approach for the analysis of the CSF mNGS-CNV technique, which facilitated the earlier diagnosis of leptomeningeal malignancy. Secondly, among the 34 patients with leptomeningeal malignancy, positive results were detected in 28 cases using CSF cytology and 24 cases using CNVs analysis, demonstrating a high degree of diagnostic consistency between the two methods. Lastly, the advantage of mNGS-CNVs analysis was its ability to provide highly specific results without the need for repeated lumbar puncture.
The timely diagnosis of leptomeningeal malignancy remains challenging, often requiring prompt CSF cytology, tumor tissue pathology, gene mutation detection, and other auxiliary examinations [21–23]. While cytology is a classical method in the diagnosis of leptomeningeal malignancy, its diagnostic accuracy may vary and heavily relies on experienced cytopathologists [22–24]. Moreover, the positive rate of cytology from a single lumbar puncture has its limitations. In certain centers, standardized procedures for CSF cytology may not be uniformly implemented. Therefore, there is a need to explore more suggestive diagnostic techniques that offer greater diagnostic accuracy for leptomeningeal malignancy.
Previous studies have demonstrated that gene profiles in CSF can provide valuable insights into CNS tumors [19, 25, 26]. Recently, researchers have found that mNGS testing of human peripheral blood, bronchoalveolar lavage fluid (BALF), CSF or other body fluids can offer clues for distinguishing between [27–29], malignancies and infectious/inflammatory diseases [30–32]. This approach was mainly based on CNV analysis, which exhibits relatively high specificity. For instance, Gu et al. [10] reported that the mNGS-CNVs had a sensitivity of 75% and a specificity of 100% in detecting malignant tumors in patients with negative results in CSF cytology and flow cytometry.
In our study, we found a moderate sensitivity and high specificity of the CSF mNGS-CNVs technique when compared with cytology, providing evidence for its feasibility and potential as an adjunctive method in the differential diagnosis of CNS tumors. Additionally, CSF mNGS analysis excluded the presence of suspicious microorganisms, aiding in the exclusion of infectious encephalitis or meningitis. In addition, mNGS-CNVs analysis required a smaller CSF volume and did not rely on the integrity of cells and repeated lumber punctures.
However, there are still some problems that need to be considered and explored seriously. There is currently no consensus on the cutoff value of CSF CNVs. In our study, we used 10 Mb as the boundary line, taking into account previous studies by Gu et al. [10, 32], resulting in a sensitivity of 70.59% under this arbitrary standard. Lowering the length boundary line to 3 Mb increased the sensitivity of CNVs detection to 76.47%. However, the determination of the CNVs length thresholds based on tumor characteristics remains unclear, necessitating further data analysis to the selection of appropriate cutoff values.
Furthermore, there exists a strong correlation between tumor purity, the aneuploidy of the genome, and CNVs [33]. Different tumor types may have different CNV patterns [34], and the detection of CNVs in certain tumor types may present challenges. In our study, the accuracy of CNVs in detecting lymphoma was low, and the underlying mechanism for this observation remain uncertain. Thus, future investigations should focus on uncovering the relationship between tumor cell DNA content, the number of chromosome CNV fragments, tumor types, and CSF CNV detection.