Many scientists and companies have recently begun using tumor free DNA as a biomarker for cancer detection. However, few studies to date have successfully found brain and spinal cord tumor free DNA in patients’ blood. Now, Johns Hopkins researchers state that they have detected cancer free DNA in cerebrospinal fluid, and the findings are published in Proceedings of the National Academy of Sciences. Researchers Detect Cerebrospinal Fluid Cancer Free DNA In the current study researchers analyzed 35 cases of central nervous system tumors, including six medulloblastomas and 29 gliomas. First, the researchers sought to identify cellular mutants of the primary tumor, whose tissue was collected during the patient’s surgery. The researchers first used targeted sequencing to find mutants in 13 tumor tissues, and then identified mutants in the remaining tumors through exome sequencing. Next, the researchers found mutants in the cerebrospinal fluid (CFS) of the patient’s primary tumor tissue using laboratory-developed SafeSeq-S sequencing technology, which detects mutations in alleles with 1 percent accuracy. Differences in cancer free DNA detectability Researchers detected high levels of cerebrospinal fluid tumor DNA from 26 patients with highly variable mutant alleles. The authors concluded that the high degree of variability among the samples may have stemmed from “location or biological factors”. Further studies found that tumor location was associated with the detectability of cerebrospinal fluid tumor DNA. Tumors located near the cerebrospinal fluid were more likely to have tumor free DNA detected than tumors in other locations. tumor DNA was undetectable in the cerebrospinal fluid of five patients whose tumor tissue was completely surrounded by brain or spinal cord. Meanwhile, a certain level of tumor free DNA was detected in the cerebrospinal fluid of 24 patients whose tumors were located close to the brain. In addition to the tumor location, the researchers found that high grade tumors were more likely to have cerebrospinal fluid tumor DNA detected than low grade tumors. Easily detected cerebrospinal fluid tumor DNA. 4 patients who had undetectable cerebrospinal fluid tumor DNA but whose tumor tissue was located near the cerebrospinal fluid were all patients with low-grade gliomas. The location of the tumors in these four patients would make surgery more dangerous. In this case, it would be ideal to detect cerebrospinal fluid tumor DNA with an unknown tumor genotype. To verify this, the researchers sequenced the whole genome of the cerebrospinal fluid of these four patients to identify the tumor DNA and compared the mutations detected by the whole genome with those detected by SafeSeq-S. The results showed that the exome sequencing failed to detect the Cerebrospinal fluid tumor DNA allele mutation probability of 1%. Opening the Door to Longitudinal Studies of Clinical Application Trials Using Cerebrospinal Fluid Tumor Genes as Biomarkers Although the discovery of cerebrospinal fluid tumor DNA is exciting, the authors of the study indicate that there is an urgent need for more sensitive, non-invasive techniques to evaluate brain and spinal cord tumors. For example, nearly 30% of glioblastoma patients undergo surgery for fear of cancer recurrence, but surgery has proven unnecessary. Although tumor free DNA was not detected at 100% in the current study, its sensitivity was equal to or better than noninvasive tests for other malignancies, and it was particularly sensitive for tumors near the cerebrospinal fluid or cortical surface. In conclusion, the researchers suggest that this study is an “exploratory study” that opens the door to a longitudinal study of cerebrospinal fluid tumor genes as biomarkers for clinical applications.