Predictive value of epidermal growth factor receptor expression for first-line chemotherapy plus cetuximab in patients with head and neck and colorectal cancer: Analysis of data from the EXTREME and CRYSTAL studies

Background: The phase III EXTREME and CRYSTAL studies demonstrated that the addition of cetuximab to chemotherapy significantly improved survival in the first-line treatment of recurrent/metastatic squamous cell carcinoma of the head and neck (SCCHN) and KRAS wild-type metastatic colorectal cancer (mCRC). In advanced non-small-cell lung cancer (NSCLC), high EGFR expression was identified as a tumour biomarker that can predict survival benefit associated with the addition of cetuximab to first-line chemotherapy. We investigated whether tumour EGFR expression level was predictive of cetuximab benefit in EXTREME and CRYSTAL study patients. Methods: Prospectively collected tumour immunohistochemistry data were used to generate an EGFR immunohistochemistry score (scale 1-300) for patients in the EXTREME and CRYSTAL studies. For each study, the association between tumour immunohistochemistry score and cetuximab benefit was investigated. The EXTREME and CRYSTAL studies are registered with Clinical Trials.gov, numbers NCT00122460 and NCT00154102, respectively. Findings: Tumour EGFR immunohistochemistry data were available for 411 of 442 (93%) patients from the EXTREME study intention-to-treat (ITT) population and 664 of 666 (100%) patients from the ITT population of the CRYSTAL study with EGFR-expressing, KRAS wild-type disease. The distribution of immunohistochemistry scores was similar between the treatment arms of each study, but differed between studies. A clinically relevant benefit for progression-free and overall survival associated with the addition of cetuximab to chemotherapy was seen across the full score range in EXTREME study patients. Similarly, CRYSTAL study patients derived a clinical benefit across the full score range, with no meaningful association between EGFR expression level and benefit. Interpretation: The addition of cetuximab to chemotherapy improved survival in the first-line treatment of recurrent/metastatic SCCHN and KRAS wild-type mCRC regardless of tumour EGFR expression level, indicating that in contrast to findings in NSCLC, EGFR expression level is not a clinically useful predictive biomarker in these settings.