Chromogenic in situ Hybridization Analysis of EGFR Gene Copies in Colon Adenocarcinoma Based on Intra-Operative Imprints and Tissue Microarrays

Abstract

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.