Epidermal growth factor receptor immunohistochemistry

• Published in: Cancer 2008-03, Vol.112 (5), p.1114-1121
• Main Authors: Hirsch, Fred R., Dziadziuszko, Rafal, Thatcher, Nick, Mann, Helen, Watkins, Claire, Parums, Dinah V., Speake, Georgina, Holloway, Brian, Bunn, Paul A., Franklin, Wilbur A.
• Format: Article
• Language: English
• Subjects: cutoff point; epidermal growth factor receptor; immunohistochemistry; nonsmall‐cell lung cancer; phase 3 trial
• ISSN: 0008-543X; 1097-0142
• DOI: 10.1002/cncr.23282

BACKGROUND The ISEL (Iressa Survival Evaluation in Lung Cancer) clinical trial evaluated the efficacy of gefitinib versus placebo in pretreated nonsmall‐cell lung cancer patients. Two different antibodies, scoring systems, and cutoff points of epidermal growth factor receptor (EGFR) protein expression were compared to predict response and survival of enrolled patients. METHODS EGFR expression was assessed in tumor samples by immunohistochemistry using the Dako EGFR pharmDx kit (scoring percent of tumor cells with positive staining) and Zymed monoclonal antibody clone 31G7 (scoring staining index derived from proportion of positive cells times staining intensity). RESULTS Data for EGFR expression were available for 379 patients for Dako and 357 patients for Zymed antibody (22% and 21%, respectively, of trial population). Objective response rates in gefitinib‐treated EGFR‐positive patients defined with various cutpoints with Dako antibody varied between 8% and 12%, and with Zymed antibody between 10% and 13%. Lower cutoff points with Dako antibody provided the best discrimination between EGFR‐positive and EGFR‐negative patients for survival hazard ratios comparing gefitinib to placebo, with a significant treatment/cutoff point interaction for 10% cutoff point (P = .049). A similar but less apparent trend was noted for Zymed antibody, although the discrimination between hazard ratios was not significant for any cutoff point analyzed. CONCLUSIONS Assessment with the Dako PharmDx kit and percentage of cells with positive staining may provide more accurate prediction of differential effect on survival with gefitinib than assessment with Zymed antibody and staining index. Using higher cutpoints to define positivity does not improve test discrimination. Cancer 2008. © 2008 American Cancer Society. Epidermal growth factor receptor (EGFR) immunostaining with the Dako PharmDx kit according to percent of cells with positive staining appears to predict for survival outcome with gefitinib better than Zymed antibody according to staining index. If EGFR immunohistochemistry is to be applied for patient selection, low cutoff levels to define protein positivity should be used.