Author of

• 10923

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  P1.18 - Poster Session 1 - Pathology (ID 175)

  • Event: WCLC 2013
  • Type: Poster Session
  • Track: Pathology
  • Presentations: 1
  • Moderators:
  • Coordinates: 10/28/2013, 09:30 - 16:30, Exhibit Hall, Ground Level

  • 10926

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    P1.18-003 - Immunohistochemical detection of Epidermal Growth Factor Receptor Mutations in Patients with Non-Small Cell Lung Cancer. (ID 855)

    09:30 - 09:30  |  Author(s): A. Bondgaard
    • Abstract

    Background
    Determination of Epidermal Growth Factor Receptor (EGFR) mutational status has pivotal impact on treatment in non-small cell lung cancer (NSCLC). A standardized test has not yet been approved. DNA sequencing has previously been regarded as gold standard method. The rather low sensitivity of this method has led to development of more sensitive, but also more complicated methods including real-time PCR (RT-PCR). Immunohistochemistry (IHC) with mutation specific-antibodies may be a promising method for detection EGFR mutations in NSCLC.

    Methods
    This case-control study includes 191 patients (36 patients with an EGFR mutation and 155 wild type (WT) patients (randomly selected)) as detected by RT-PCR (Therascreen EGFR PCR kit, Qiagen, UK). This method identifies 29 somatic mutations from exons18-21 with a sensitivity of 1%. For EGFR IHC, antibodies against mutations in exon19 (clone 6B6) and exon21 (clone 43B2) by Cell Signaling Technology (USA) were used. All specimens were visualized according to the standardized protocol of EnVision FLEX+ system (DAKO, DK).The protein expression for each specimen was evaluated and a H-score, including intensity (graded 0-3) and percentages (0-100) of stained malignant cells, was calculated. A positive tumor was defined by a H-score value>0. The sensitivity (true positive/(true positive + false negative) and specificity (true negative/(true negative + false positive) were evaluated with the results from Therascreen EGFR PCR kit as reference.

    Results
    The sensitivity and specificity of the mutation-specific antibodies are presented in Table1.

    	Sensitivity (%)	95% CI	Specificity (%)	95% CI
    Exon19del(E746-A750)	60.0	32.3-83.4	99.3	96.3-100
    Exon21(L858R)	87.5	47.4-99.7	97.4	93.5-99.3

    Table1: Performance of the EGFR mutation-specific antibodies. CI = confidence interval, Del = deletion. For mutations in exon19, 5 specimens were false negative (IHC-, RT-PCR+) and 1 was false positive (IHC+, RT- PCR-). For mutations in exon21, 3 samples were false negative and 3 were false positive. 1 false positive for exon21 had maximal H-score (300).

    Conclusion
    We demonstrated a high specificity for IHC with mutation-specific antibodies for detecting EGFR mutations in patients with NSCLC. However, the sensitivity was low, especially for del19-mutations, and thus these antibodies are not yet ready as a screening method for detection of these mutations. We used RT- PCR as reference. This method is very sensitive compared to conventional Sanger sequencing being able to detect mutations present in 1% of the malignant cells. Some studies in NSCLC have questioned whether detection of such a small fraction of malignant tumor cells has clinical relevance for treatment of the whole tumor. The mutation-specific antibodies might be compared to highly sensitive methods, including RT-PCR and validated in clinical trials in order to detect the clinical impact of both methods.