EGFR-immunohistochemistry in colorectal cancer and non-small cell lung cancer : Comparison of 3 commercially available EGFR-antibodies

Background : Epidermal Growth Factor Receptor (EGFR)- targeted therapies are currently used for the treatment of metasta- sized colorectal cancer (CRC) and non small cell lung cancer (NSCLC). Patient selection for this treatment is based on immuno- histochemical (IHC) testing for EGFR. The rising amount of commercially available EGFR-antibodies makes standardisation of EGFR-IHC necessary. The goal of this study was to analyse possible discrepancies between 3 antibodies against EGFR. Patients and methods : 36 formalin-fixed samples of CRC (n = 26) and NSCLC (n = 10) were stained with 3 antibody-clones : 2- 18C9 (DakoTM); 31G7 (VentanaTM) and 111.6 (Labvision NeomarkersTM). Interpretation of stains includes assessment of % positive cells, evaluation of cut off values and staining intensity. Results : With a 1% cut-off, the 2-18C9 clone stained 86% of the cases positive, the 31G7-clone 77% and the 111.6-clone 52%. With a 10% cut-off, percentages declined to 77%, 61% and 30% respectively. The 2-18C9-clone showed the highest staining intensity. The 2-18C9 clone and the 31G7-clone showed a concor- dance rate of 90%. Conclusions : IHC staining with 3 different antibody clones directed against EGFR shows indeed differences in staining results : the percentage of positive cells and staining intensity are variable. A correct cut-off value for a positive result is important and can be different depending upon the antibody. Appropriate validation of an antibody is essential before it can be used for selection of patients. (Acta gastroenterol. belg., 2008, 71, 213-218).