BIOM-02. CSF LIQUID-BASED DIAGNOSIS OF LEPTOMENINGEAL DISEASE (LMD) FROM NON-SMALL CELL LUNG CANCER (NSCLC) USING DDPCR AGAINST EGFR MUTATIONS

Abstract

Abstract Leptomeningeal disease (LMD) due to spreading of solid cancers to the leptomeninges has a very poor prognosis and is poorly diagnosed. MR imaging may be negative and CSF cytology, the gold standard, is not sensitive enough, due to small number of cells inherent in CSF, small volume and inter-observer variability in microscopy. We tested the hypothesis that cfDNA from CSF could be a unique source of DNA from LMD which can be used for diagnosis as well as research. We collected 39 CSF samples from patients suspected of LMD from NSCLCs. CfDNA was extracted by cobas® cfDNA Sample Preparation Kit. Hotspot EGFR mutations (G719X, S768I, T790M, C797S, L858R, L861Q, and 19 del) were tested by multiplexed droplet-digital PCR (ddPCR). EGFR mutation status of the original primary NSCLCs were previously tested for by real-time PCR using formalin-fixed paraffin-embedded tissues. Six samples did not yield sufficient DNA. For the remaining 33 cases, EGFR mutations were detected in 16 samples. For fifteen of these positive cases, identical mutations were found in the matched tissue samples. EGFR status of one primary tumor was unknown. Cytology was negative in 10 cases, atypical in five and only positive in one case. For the 17 negative samples, in 11 cases, the corresponding tumor tissues lacked EGFR mutations. Five patients from the negative group were eventually found not to have LMD. Only in one case was the lung tissue found to have EGFR mutation but mutation was not found in CSF cfDNA. In a few selected cases, we studied the genomics of the cfDNA together with the primary tumor tissues with low-pass WGS and similar CNVs were found in both. CSF cfDNA is a unique source of DNA from LMD and can be used as a useful tool in clinical diagnosis and research.