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M. Del Grammastro



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    ORAL 38 - Liquid Biopsies (ID 147)

    • Event: WCLC 2015
    • Type: Oral Session
    • Track: Biology, Pathology, and Molecular Testing
    • Presentations: 1
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      ORAL38.07 - Quantification of EGFR Mutations in Plasma of NSCLC Patients: An Early Predictor of Clinical Response to Tyrosine Kinase Inhibitors (ID 2242)

      17:50 - 18:01  |  Author(s): M. Del Grammastro

      • Abstract
      • Presentation
      • Slides

      Background:
      As DNA analytical methods have become more sensitive, attempts to develop accurate clinical tests to assess tumor mutation status by means of patient plasma samples are now being pursued. The potential to accurately quantify EGFR mutations in plasma from non-small cell lung cancer (NSCLC) patients would enable more rapid and more frequent analyses to assess disease status; however, the utility of such analyses for clinical purposes has only recently started to be explored.

      Methods:
      Plasma samples were obtained from 69 NSCLC patients with EGFR-mutated tumors and 21 negative control cases. EGFR mutations in plasma were analyzed by a standardized allele-specific polymerase chain reaction (PCR) test and ultra-deep next generation sequencing (NGS). A semi-quantitative index (SQI) was derived from dilutions of known EGFR mutation copy numbers. Clinical responses were evaluated by RECIST 1.1 criteria and expressed as percent tumor shrinkage.

      Results:
      The sensitivity and specificity of the PCR test and NGS assay in plasma versus tissue were 72% versus 100%, and 74% versus 100%, respectively. Quantitative indices by the PCR test and NGS were significantly correlated (P<0.001). EGFR testing at baseline and serially at 4–60 days during TKI therapy revealed a progressive decrease in SQI , starting from day 4, in 95% of cases. The rate of SQI decrease correlated with percent tumor shrinkage at 2 months (P<0.0001); at 14 days it was more than 50% in 70% of patients (rapid responders) (Fig.1A-B). In 2 patients with slow response (Fig.1B), an early increase in the circulating levels of the T790M mutation was observed. These patients were defined as early resistant (Fig.1C). No early T790M mutations were seen in plasma samples of rapid responders, suggesting that slow responders are more prone to develop early resistance.

      Conclusion:
      Quantification of EGFR mutations from plasma with a standardized PCR test is feasible. To our knowledge, this is the first study showing a strong correlation between the EGFR SQI during therapy and clinical response with relevant implications for patient management. With the strong correlation between EGFR SQI in plasma and clinical outcome, this study opens the way to prospectively design clinical trials to confirm these data and evaluate the diagnostic value of this test. Figure 1



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