Controversial evaluation of EGFR protein and gene status in predicting response to anti-EGFR monoclonal antibodies in metastatic colorectal cancer: a case report and review of the literature

Abstract

Clinical studies showed that only 10% of patients with metastatic colorectal cancer (mCRC) respond to treatment with the anti-epidermal growth factor receptor (EGFR) monoclonal antibodies panitumumab or cetuximab, regardless of the line of treatment. The current tool used to select patients, i.e. immunohistochemistry (IHC) evaluation of EGFR expression by EGFR pharmDx™ Kit, is not reliable in predicting response. Retrospective analyses of factors such as increased EGFR gene copy number and KRAS and/or BRAF mutations showed that such molecular changes could affect clinical benefit from anti-EGFR monoclonal antibodies. We report here the case of a 66-year-old man with chemorefractory mCRC, considered not eligible to salvage treatment with the anti-EGFR monoclonal antibody cetuximab and irinotecan because the primary adenocarcinoma of the rectum was found not expressing EGFR protein by IHC. However, FISH analysis of EGFR gene copy number and evaluation of KRAS and/or BRAF specific mutations by gene sequencing showed characteristics associated with favourable clinical outcome to anti-EGFR therapy. Based on the EGFR protein expression by IHC in a liver metastasis, the patient was then treated with cetuximab plus irinotecan, obtaining symptoms improvement and a dramatic objective tumor response in all sites of disease, lasting 4.2 months. We also discuss literature findings about the role of different biological characteristics in predicting clinical benefit from anti-EGFR therapy in patients with mCRC.