Heterogenous high-level HER-2 amplification in a small subset of colorectal cancers

HER-2 is the molecular target for antibody-based treatment of breast cancer (trastuzumab). The potential benefit of anti-HER-2 therapy is currently investigated in several other HER-2 amplified cancers. For example, trastuzumab was recently shown to be effective in HER-2 positive gastric cancer. To address the potential applicability of anti-HER-2 therapy in colorectal cancer, tissue microarray sections and colorectal resection specimens of 1851 colorectal cancers were analyzed for HER-2 overexpression and amplification using FDA approved reagents for immunohistochemistry and fluorescence in situ hybridization. HER-2 amplification was seen in 2.5% and HER-2 overexpression in 2.7% of 1439 interpretable colorectal cancers. Amplification was often high level with HER-2 copies ranging from 4 to 60 per tumor cell and was strongly related to protein overexpression. HER-2 amplification and overexpression were unrelated to histological tumor type, tumor localization, grading, pT, pN, pM or survival. As heterogeneity of drug target expression could represent a major drawback for targeted cancer therapy we next studied HER-2 heterogeneity in selected cases. Extensive evaluation of all available large sections from patients with HER-2 positive colorectal cancer revealed heterogenous findings in 3 of 4 cases. In summary, high-level HER-2 amplification occurs in a small fraction of colorectal cancers. Heterogeneity of amplification may limit the utility of anti- HER-2 therapy in some of these tumors and therefore, adequate clinical trials are needed to further evaluate this approach.