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MINI 07 - ChemoRT and Translational Science (ID 110)
- Event: WCLC 2015
- Type: Mini Oral
- Track: Treatment of Locoregional Disease – NSCLC
- Presentations: 1
MINI07.04 - Dynamic Changes in Cell-Free Circulating Tumor DNA to Track Tumor Response and Risk of Recurrence in Stage III Non-Small Cell Lung Cancer (ID 2499)
16:45 - 18:15 | Author(s): T. Buchholz
While the curative management of unresectable stage III non-small cell lung cancer (NSCLC) is definitive chemoradiotherapy, clinical outcomes remain poor. Cellular heterogeneity in tumors is correlated with therapeutic resistance and poor prognosis. We hypothesize that tumor-specific mutant allelic frequency in cell-free DNA from plasma quantifies tumor heterogeneity and that tracking allelic evolution via blood from patients during and after treatment can serve as a non-invasive means to monitor treatment response and recurrence.
Between 2009-2013, 156 patients with unresectable NSCLC who received definitive radiotherapy or chemoradiotherapy were consented to have blood drawn at baseline before starting radiotherapy, once or twice during treatment, and once or twice during follow up visits. Cell-free plasma DNA was sequenced using a cell-free circulating tumor DNA (ctDNA) next generation sequencing (NGS) assay (Guardant360) that uses digital sequencing to report single nucleotide variants (SNVs) in 68 genes and amplifications in 16 genes. This ctDNA assay has high sensitivity (detects 85%+ of the SNVs detected in tissue in advanced cancer patients) and analytic specificity (>99.9999%). Over 670 serial samples were collected from these patients. Here we report the initial analysis of the first 26 patients of this ongoing study.
Among this initial cohort, 23 (88%) had a recurrence (PFS ranged from 1.2 – 27.9 months) and three (12%) had no evidence of recurrence as of last contact (32.8 – 42.8 months post-radiotherapy completion). Twenty-one patients (81%) had ctDNA alterations present pre-radiotherapy, of which six had a classic driver mutation: KRAS G12F x2; KRAS G12S; PIK3CA E545K x2; PIK3CA H1047R. These six patients had significantly shorter PFS compared to patients without a driver mutation present pre-radiotherapy: average PFS of 4.2 months (1.2 - 8.3) vs. 18.6 months (4.4 - 42.8) respectively (p=0.002). All six had the driver mutation disappear during radiotherapy, four had new alterations appear during and/or post-treatment. One patient had the driver mutation reappear in ctDNA post-radiotherapy and had the shortest PFS (1.2 months) of all patients. Ten patients (38%) had no ctDNA alterations present in the post-radiotherapy blood sample and a trend was observed of improved PFS among patients without ctDNA alterations post-treatment (average PFS 52.3 vs. 75.5 months respectively) however this was not statistically significant (p=0.1). Of note, the three patients without evidence of recurrence as of last contact had no ctDNA alterations identified in the post-treatment sample. This trend is anticipated to become significant with larger sample size.
In this interim analysis, we found that the dynamic alterations of specific mutant alleles strongly correlated with clinical response and that persistence of ctDNA mutant allele concentrations post-definitive treatment is likely a marker of early metastatic recurrence. Undetectable ctDNA in post-treatment sample was seen in the three patients with approximately three years of PFS. These initial results suggest that serial ctDNA analysis may be useful to monitor treatment response and identify patients at high risk for early recurrence who may benefit from additional systemic therapy.
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