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ORAL 38 - Liquid Biopsies (ID 147)
- Event: WCLC 2015
- Type: Oral Session
- Track: Biology, Pathology, and Molecular Testing
- Presentations: 1
ORAL38.06 - Identification of Actionable Tumor Alterations in Circulating Cell-Free Tumor DNA (cf DNA) Using Digital Sequencing from NSCLC Patients (ID 1706)
16:45 - 18:15 | Author(s): S.A. Mortimer
To fully implement precision therapy in lung cancer, transition to a re-biopsy policy will be required at baseline and at progression after each line of therapy. The molecular testing paradigm is shifting toward next generation sequencing (NGS). As tissues are limited and repeat invasive biopsy introduces cost and risk, novel technologies sensitive and specific enough for multiplexed assessment in cell-free DNA (cfDNA) isolated from patient blood would represent a significant advance. Preliminary experience from investigators suggest a high degree of correlation between repeat tumor biopsy and plasma NGS. Here, we present the Guardant Health (GH) digital sequencing approach in a consecutive series of NSCLC cases.
225 consecutive blood specimens from NSCLC patients, collected February–March 2015, were evaluated for cfDNA tumor alterations by digital sequencing using the GH panel of 68 genes. The test includes all reported fusion partners for ALK, RET, ROS1, and NTRK1 and cfDNA amplification for 16 genes. The mutant allele fraction (MAF) was calculated relative to WT in cfDNA. The test is sensitive to a single fragment of mutated cfDNA in a 10 ml blood sample and analytic specificity is >99.9999%.
Canonical EGFR activating mutations were detected in 20 cases (14 E19del, 3 L858R, 2 E20ins, 1 G719A). EGFR T790M co-occurred in 7 cases (6 E19del, 1 L858R), with EGFR amplification observed in 6 of the 20. Median age for patients with EGFR mut+ was 62.5; 18 female(90%), compared to nonEGFR-mutant cases. Four cases had driver fusions (2EML4-ALK, 2 KIF5B-RET) and five cases harbored an ERBB2 E20ins. KRAScodon 12/13 mutations were detected in 23 patients, while 3 harbored mutations in HRAS(Q61L) and NRAS(Q61L, G13R), and 6 had BRAF mutations (4 V600E, 2 G466X). All putative drivers were mutually exclusive. Mutations in signal transduction factors with confirmed gain-of-function activity included AKT1(E17K), MEK1(K57N, C121S), PIK3CA(E542K, E545K x2, H1047L, M1043V, R93W) and JAK2(V617F x2); truncating or missense mutations (>3% MAF) were observed in NF1 (6 cases), PTEN(1 case), SMAD4(4 cases) and STK11(4 cases). TP53 mutations were detected in 116/225 (51%). Evidence of gene amplification was seen in 32 cases, with 11 harboring multiple events. By function, amp events were observed for G1 cell cycle factors:11, RTKs: 17, MYC: 2; and signal transduction: 21. MAF ranged from 0.06% to 83.4% (av 5.1%; median: 9.8%), reflecting clinical and biologic diversity of patients. In a clinical subset at UC Davis, 27 patients were evaluated and alterations were detected in 18 (66.7%). Actionable findings were identified in 14 (77.8%) including 2 with EGFRL858R, 1 with EGFR E19del, and 1 interesting case with EGFR E19del at 45% MAF, EGFR amplification, and an emerging EGFR T790M clone at 0.54% MAF.
In a series of NSCLC cases, high-sensitivity, high-specificity cfDNA analysis demonstrated the ability to identify somatic tumor alterations, including clinically actionable predictors, in a majority of patients via a simple blood draw, suggesting that this approach can be used for guiding therapeutic decision-making when repeat biopsy is high risk or not possible. Assuming validation, plasma cfDNA analysis may supplant invasive tumor biopsy in the near future.
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