Analysis Of HER2 Oncogene And Chromosome 17 By Dual-probe Chromogenic And Fluorescence In Situ Hybridizations In Breast Cancer

Carcinomas of the breast are the most frequent cancers of women, with the highest mortality.Targeted therapy with trastuzumab (Herceptin) has had major impact on the adjuvant therapy of breast cancer.However, trastuzumub is effective only in those breast cancer with amplified HER2 oncogene or showing overexpression of the HER2 protein, in addition, trastuzumab therapy is expensive and associated with rare but severe cardiotoxic effects. Therefore, it has become mandatory to assess the HER2 status of all newly diagnosed bresst cancers to saaess eligibility for the treatment. Immunohistochemistry (IHC) is the mostly used method for HER2 testing However, recent data from the American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) indicates that as many as 20% of HER2 assessments performed by IHC ( supplemented by FISH analysis of IHC 2+ cases ) may be inaccurate. It has been reported that IHC is prone to producing a significant number of false-positive results, as well as a smaller number of false-negative results. FISH is now regarded as the gold standard for HER2 testing in the world.The aim of this investigation was to evaluate the clinical application of dual-probe chromogenic in situ hybridization (dual-probe CISH) in the testing of HER2 gene status in breast cancer patients by comparison with fluorescence in situ hybridization ( FISH ) . The potential impact of chromosome 17 polysomy in the dertermination of HER2 status was also evaluated.We collected 146 paraffin-embedded tissue sections of breast cancer and determined HER2 gene and chromosome 17 copy numbers using CE approved commercial kits of dual-probe FISH ( for 146 cases) and dual-probe CISH ( for 115 cases), respectively. The results were interpreted based on 2007, ASCO/CAP either HER2 gene copy number or the ratio of HER2/chromosome 17 centromere (HER2/CEN17).We seclected one case of invasive breast cancer randomly, the ratio of the three times dual-probe CISH is 0.57±0.07,reapectively, while the ratio of FISH is 0.65. Of the 83 cases measured by both FISH and dual-probe CISH methods, the concordance between two methods for negative and positive results was 92.7% and 97.7%, respectively, while the overall concordance between the two methods was 96.4%. Of the 146 cases measured by FISH, 13 cases were interpreted as equivocal if only HER2 copies were counted, which was 1.6-fold (13/8) higher than the equivocal cases interpreted by counting the ratio of HER2/CEN17. Moreover, 3 (4.8%) of 63 HER2 positive cases determined by HER2 copies turned out to be HER2 negative determined by the ratio of HER2/CEN17, in dual-probe CISH results, 1 (1.8%) of 57 positive cases was turned to negative by the comparison of two corresponding scoring methods. In FISH and dual-probe CISH, the incidence of the positive cases determined by HER2/CEN17 became equivocal determined by HER2 copy numbers is 4.8%( 3/63 )and 6.7% (4/60) .In addition, we also observed from FISH results that there were more chromosome 17 polysomy cases (63.5%, 40/63) in HER2 positive subgroup than those (37.3%, 28/75) in HER2 negative subgroup. (p=0.002).It is the first time to analyse the HER2 status by dual-probe CISH and FISH.Our HER2 results determined by dual-probe CISH method were almost perfect agreed with the corresponding results determined by FISH method, indicating dual-probe CISH is a reliable alternative to FISH in HER2 testing. This study also indicate that the test accuracy may be improved when HER2 and chromosome 17 are simultaneously tested and counted.