Protocol modifications influence the result of EGF receptor immunodetection by EGFR pharmDx in paraffin-embedded cancer tissues.

EGF receptor (EGFR) became a useful target for several recently introduced therapies of various cancer types including colorectal, lung, head and neck cancers and glioblastoma. The successful clinical application of these novel molecularly targeted therapies requires the expression of their target, EGFR, determined by nucleic acid based or immunohistochemical techniques. However, until now, immunohistochemistry has not become a reliable diagnostic approach for this purpose. The golden standard for the determination of EGFR protein expression in paraffin-embedded cancer tissues is the EGFR pharmDxTM kit. Here we show that the recommended protocol may not be optimal for EGFR immunodetection. Microwave antigen retrieval and extended primary antibody incubation time converted four out of eight EGFR-negative tumors into EGFR-positive in a study of 50 lung adenocarcinoma cases. Accordingly, we recommend retesting cases negative for EGFR with EGFR pharmDxTM using protocol modifications optimizing antigen retrieval and the incubation periods.