Her-2/neu gene amplification, elevated mRNA expression, and protein overexpression in the metaplasia-dysplasia-adenocarcinoma sequence of Barrett's esophagus

The importance of alterations of the Her-2/neu oncogene in the tumorigenesi s of Barrett's adenocarcinoma (BCA) is discussed controversially. In the pr esent study, we evaluated for the first time the Her-2/neu status in the me taplasia-dysplasia-adenocarcinoma sequence of BCA simultaneously at the DNA , mRNA, and protein level using resection specimens of 25 patients. The loc us-specific Her-2/neu gene status was quantified by performing fluorescence in situ hybridization, and information about the ploidy status of chromoso me 17 was obtained. Tissue sections from the same areas were used for quant itative RT-PCR (TaqMan RT-PCR) of laser-microdissected tumor cells and for immunohistochemistry to quantify Her-2/neu mRNA and oncoprotein expression. Her-2/neu gene amplification was observed in 35% of BCA, and all of these samples showed strong overexpression of both mRNA and oncoprotein. A polyso my 17 without Her-2/neu gene amplification was Observed in 52% of BCA, show ing a normal or moderately elevated mRNA expression and no or weak immunopo sitivity. From 13 areas of high-grade dysplasia (HGD) we found four to be a mplified for the Her-2/neu locus, whereas five showed a polysomy 17. All fo ur samples of HGD areas with Her-2/neu gene amplification displayed mRNA an d strong oncoprotein overexpression; however, lower mRNA levels were seen t han in the amplified BCA areas. None of the samples with low-grade dysplasi a (LGD) showed a locus-specific Her-2/neu amplification, but polysomy 17 wa s present in four of eight cases. No changes were detected in BCA-associate d intestinal metaplasia and squamous epithelium. In summary, only a locus-s pecific Her-2/neu gene amplification was associated with strong mRNA overex pression and strong membranous Her-2/neu immunostaining in BCA and HGD. A c hromosome 17 polysomy, as found in the majority of EGA, led to no or weak m RNA overexpression and no or weak immunopositivity, in the metaplasia-dyspl asia-adenocarcinoma sequence, a chromosome 17 polysomy without Her-2/neu ge ne amplification was already present in LGD. This may be a result of an ear ly polyploidization, preceding the later genetic events, such as Her-2/neu gene amplification in HGD and BCA.