1307PD - Detection of driver and resistance mutations in leptomeningeal metastases of NSCLC by next-generation sequencing of cerebrospinal fluid circulating tumor cells

Abstract

Background: Leptomeningeal metastases (LM) are more common in non-small cell lung cancer (NSCLC) with EGFR mutations. The diagnosis is difficult by traditional imaging only, and leads to poor understanding of resistance mechanisms of LM. Methods: We compared the CellSearch Assay™, the Thinprep cytologic test (TCT), and brain magnetic resonance imaging (MRI) in 21 NSCLC patients with suspected LM. Next-Generation sequencing that included 416 cancer-associated genes was also performed on cerebrospinal fluid circulating tumor cells (CSFCTCs) of 19 patients. Results: Twenty-one patients were diagnosed with LM, and CSFCTCs were captured by CellSearch in 20 patients (median, 969 CSFCTCs/7.5 mL; range, 27–14,888). CellSearch had a sensitivity of 95.2% for LM diagnosis, which was higher than that of TCT (12/21, 57.1%), MRI (10/21, 47.6%), and MRI plus TCT (19/21, 90.5%), respectively. CTCs were found only in 5 of 14 patients (median, 2 CTCs/7.5 mL; range, 2–4), which was a much lower ratio than CSFCTCs. Genetic profiles of CSFCTCs were highly concordant with molecular mutations identified in the primary tumor (17/19, 89.5%). The resistance gene EGFR T790M was detected in 7 of 9 patients with extracranial lesions, but was only detected in 1 of 14 CSFCTCs samples. Other potential resistant mutations such as MET amplification and ERBB2 mutation were also identified in CSFCTCs.Table1307PDPatient No.Primary gene profileTargeted therapy before LMRebiopsy gene profileCSFCTCs gene profile (NGS)1EGFR L858R (lung)ErlotinibEGFR L858R (lung, ARMS); MET(IHC):80% (3+)EGFR L858R2bEGFR del19 (lymph node)IcotinibUAEGFR del19; EGFR T790M3EML4-ALK (lung)CrizotinibEML4-ALK (pleural effusion)EML4-ALK; MET amplification4EGFR 20INS (lung)NoneUAEGFR 20INS5EGFR del19 (pleura)GefitinibEGFR del19 and T790M (lung)EGFR del19; EGFR amplification6EGFR L858R (lung)ErlotinibEGFR L858R and T790M (lung)EGFR L858R7EGFR, ALK (WT)NoneSnapshot, MET, KIT (WT)Common driver gene (WT)9EGFR del19 (pleura)GefitinibEGFR del19 and T790M (liver);MET: 100% (3+) (liver)EGFR del19; ERBB2 exon8 T328fs; ROS1 exon7 W215X10EGFR L858R (lung)Gefitini, erlotinibEGFR del19 and T790M (lung)EGFR del1911EGFR L858R (lung)Gefitini, erlotinibUAEGFR L858R12EGFR L858R (lung)GefitinibEGFR L858R and T790M (plasma)Common driver gene (WT)13EML4-ALK (lung)CrizotinibUAEML4-ALK14EGFR del19 (lung)Erlotinib, afatinibUAEGFR del19; MET amplification15EGFR del19 (lung)IcotinibUAEGFR del1916EGFR L858R (lung)NoneEGFR L858R (lymph node)EGFR and ALK (WT); RET exon4 V253E17EGFR L861Q (lymph node)ErlotinibUAEGFR L861Q; EGFR del1918cEGFR L858R (lung)GefitinibEGFR L858R and T790M (lung)EGFR L858R; PIK3CA exon2 N107S; MET exon11 F839L19EGFR L858R (lung)GefitinibEGFR L858R and T790M (lung)EGFR L858R21EGFR L858R (lung)GefitinibUAEGFR L858R Open table in a new tab Conclusions: CellSearch could be a more sensitive method for detecting tumor cells in CSF, and potentially provides earlier diagnosis of LM. More importantly, CSFCTCs could be an important and new way of “liquid biopsy” for genetic profiles of metastatic tumor cells in LM patients of NSCLC. Legal entity responsible for the study: Yi-Long Wu Funding: Geneseeq Biotechnology, Inc., Nanjing, China Disclosure: All authors have declared no conflicts of interest.