Impact of polysomy 17 of breast cancer on the testing results of human epidermal growth factor receptor 2(HER-2) and its clinicopathological significance

Objective:To investigate the impact of polysomy 17 of breast cancer on testing results of human epidermal growth factor receptor 2(HER2) and its clinicopathologic significance.Methods:Seventy-one patients with primary invasive breast carcinoma were studied.The HER2 gene and chromosome 17 copy numbers were determined by dual-color fluorescence in situ hybridization(FISH).The testing results were expressed by ABSolute HER2 gene copy number or the ratio of HER2 to chromosome 17.Based on the FISH testing results and HER2 protein expression determined by immunohistochemistry the results were compared between different groups divided by related clinicopathologic parameters.Results:All patients who had doubtable FISH results,either by ABSolute HER2 copy number(14 of 71 patients;19.7%) or by the ratio HER2/chromosome 17(2 of 71 patients,2.8%),displayed polysomy 17.Polysomy 17-positive patients had no significant difference with HER2-negative patients in tumor grade,lymph node metastasis,and estrogen receptor(ER) expression(all P0.05);but compared with HER2-positive patients,they showed lower tumor grade(50.0% vs 81.5%,P=0.025),higher rate of negative lymph node(55.6% vs 25.9%,P=0.045),and higher rate of ER positive expression(83.3% vs 41.7%,P=0.005) and progesterone receptor(PR)positive expression(87.5% vs 44.4%,P=0.003).Conclusion:Compared with HER2 gene amplification group,polysomy 17-positive group tends to have negative HER2 gene expression.Polysomy 17 influences the testing results of HER2 and may be the main factor that caused doubtable results in FISH examination.