This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Personeni, N. Articles by Tejpar, S. PubMed PubMed Citation Articles by Personeni, N. Articles by Tejpar, S.

Clinical Usefulness of EGFR Gene Copy Number as a Predictive Marker in Colorectal Cancer Patients Treated with Cetuximab: A Fluorescent In situ Hybridization Study

Authors' Affiliations: ¹ Digestive Oncology Unit and ² Department of Morphology and Molecular Pathology, University Hospital Gasthuisberg, ³ Biostatistical Centre, and ⁴ Center for Human Genetics, Katholieke Universiteit Leuven, Leuven, Belgium; ⁵ Service de Gastro-entérologie, Cliniques Universitaires Saint-Luc, Université Catholique de Louvain; ⁶ Department of Gastroenterology, GI cancer Unit, Erasme University Hospital, Université Libre de Bruxelles; ⁷ Clinique des Pathologies Tumorales du Côlon et du Rectum, Centre du Cancer, Cliniques Universitaires Saint-Luc, Université Catholique de Louvain, Brussels, Belgium; and ⁸ Digestive Oncology Unit, Ghent University Hospital, Ghent, Belgium

Requests for reprints: Sabine Tejpar, Digestive Oncology Unit, University Hospital Gasthuisberg, Herestraat 49, 3000 Leuven, Belgium. Phone: 32-16-344218; Fax 32-16-344419; E-mail: Sabine.Tejpar{at}uz.kuleuven.ac.be.

Purpose: To evaluate the usefulness and the pitfalls inherent to the assessment of the epidermal growth factor receptor (EGFR) gene copy number (GCN) by fluorescence in situ hybridization (FISH) for outcome prediction to cetuximab in metastatic colorectal cancer. The value of testing KRAS mutation status, in addition to EGFR GCN, was also explored.

Experimental Design: FISH analysis of 87 metastatic colorectal cancer patients treated with cetuximab was done, recording individual GCN per cell and using different samples per tumor. Performances of published cutoff points and different summaries of EGFR GCN distribution were assessed for response prediction.

Results: In our data set, two published cutoff points performed less well than in their training set, yielding positive predictive values and negative predictive values between 40.0% and 48.3% and between 81.0% and 86.5%, respectively. Among summaries of GCN distribution explored, mean and right-tailed distribution of GCN yielded the highest performances. A mean EGFR GCN 2.83 provided an area under the curve of 0.71. Important heterogeneity of repeated measures of mean EGFR GCN was observed within tumors (intraclass correlation, 0.61; within-class SD, 0.40), leading to potential misclassifications of FISH status in 7 of 18 (38.8%) patients if a cutoff point were used. In multivariable analysis, EGFR GCN testing provided significant information independent of the KRAS status to predict response (P = 0.016) and overall survival (P = 0.005).

Conclusions: We confirm the association between increased EGFR GCN and outcome after cetuximab. However, because of reproducibility concerns, any decision making based on published cutoff points is not warranted.