Chromogenic in situ hybridization analysis of EGFR gene copies in colon adenocarcinoma based on intra-operative imprints and tissue microarrays.

BACKGROUND Although Epidermal Growth Factor Receptor (EGFR) over expression is a frequent event in colon adenocarcinoma (CA), identification of EGFR gene deregulation mechanisms--combined to k-ras mutations--remains the basic criterion for rational application of anti-EGFR targeted therapeutic strategies. AIM To detect EGFR gene numerical alterations in CA based on a combination of intra-operative imprints and the corresponding tissue microarrays. METHODS 60 paraffin embedded primary CAs were cored at 1.5 mm diameter and transferred to the final microarray block. Chromogenic in situ hybridization (CISH) was performed using EGFR gene and chromosome 7 centromeric probes in the tissue microarray and also in the corresponding intra-operative imprints. RESULTS CISH analysis detected 4/60 (6.6%) EGFR gene amplified cases, whereas chromosome 7 aneuploidy was identified in 11/60 (18.3%) cases. Significant association was established by correlating stage to chromosome 7 (p=0.024). A high value of concordance (kappa=1) was observed comparing overall gene status based on the tissue cores and the corresponding imprints, whereas EGFR/CEN 7 copies were more numerous in imprints than in tissue microarrays (p=0.03). CONCLUSIONS Intra-operative imprint cytology provides accurate and fast results in detecting EGFR gene/chromosome 7 centromeric signals by CISH due to the nuclear integrity and monolayer formation of the examined cells. Based on this molecular analysis, gastroenterologists and oncologists can handle those patients in a rational way regarding targeted therapies. Furthermore, chromosome 7 aneuploidy is associated with a more advanced stage in CA.