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  MO21 - Prognostic and Predictive Biomarkers V - EGFR (ID 98)

  • Event: WCLC 2013
  • Type: Mini Oral Abstract Session
  • Track: Medical Oncology
  • Presentations: 1
  • Moderators:D.C. Lam, S.M. Lee
  • Coordinates: 10/30/2013, 10:30 - 12:00, Bayside Auditorium A, Level 1

  • 12948

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    MO21.08 - Detection of EGFR mutations in plasma and diagnosis biopsies from non-small cell lung cancer patients using allele-specific PCR assays. (ID 2248)

    10:30 - 12:00  |  Author(s): H. Hager
    • Abstract
    • Presentation
    • Slides

    Background
    EGFR TKI sensitizing mutations from plasma prior to treatment were shown to be a potent predictor for survival outcome of advanced NSCLC (T. Mok, ASCO 2013). In this study, we tested EGFR mutations in the archived plasma from 199 advanced adenocarcinoma. The plasma samples were taken when they progressed on their chemotherapy and before their 2nd erlotinib treatment a mean of 10.5 months after the diagnostic biopsy was obtained. EGFR mutations detected in plasma after chemotherapy and in the tumor DNA from their original diagnostic biopsies were also compared.

    Methods
    Plasma DNA and tumor DNA were tested with two allele-specific PCR assays, cobas® EGFR_ FFPET tissue test and cobas® EGFR_blood test (in development at Roche Molecular Systems, Inc.). Both allele-specific PCR assays detect 41 mutations in exon 18-21 of the EGFR gene including TKI sensitizing mutations (Exon 19 deletions, L858R and G719X), resistance mutation (T790M) and atypical mutations (S768I and Exon 20 Insertions). cobas® EGFR_blood test also detects L861Q. Plasma samples of all 199 adenocarcinoma were collected immediately (less than 2 days) prior to the patient’s erlotinib treatment and stored at -80°C. From 197 (99%) of 199 of the patients tumor DNA was extracted from the diagnostic biopsy.

    Results
    Among 199 advanced adenocarcinoma patients, 24/199 (12%) were EGFR mutation positive in plasma. 28/196 (14%) were EGFR mutation positive in tumor DNA. The comparison of EGFR mutation in plasma and tumor DNA is shown in the table 1. The overall concordance of EGFR mutation status in plasma and tumor biopsy was 91% (179/196). 17/196 (9%) patients had the same EGFR mutations in plasma as in their original diagnosis biopsy and 162/196 (82%) patients were mutation negative in both samples. In this study, different EGFR mutation status in plasma and original biopsy was observed in 17 of 196 (9%) patients. 6 of 17 were EGFR mutation positive in plasma only and 11 of 17 were EGFR positive in tumor DNA only. These differences could reflect alterations in the tumor cells between sampling of biopsy and blood (average of 10.5 months) where the patients are treated with chemotherapy. Another possibility is limitations of assay technology with circulating cell-free DNA in plasma or heterogeneity of tumor.

    Conclusion
    Tumor mutations in the patient’s original diagnostic biopsy can be detected in their plasma when they progress on chemotherapy which may provide another opportunity for mutation testing. Table 1. Comparison of EGFR mutations detected in plasma and diagnostic biopsy. MND=Mutation-Not-Detected.Figure 1

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