Assessment and significance of human epidermal growth factor receptor 2 gene status in breast cancer with polysomy of chromosome 17

Abstract

To explore the impact of polysomy of chromosome 17 on the interpretation of human epidermal growth factor receptor 2 (HER2) status and its clinical significance in breast cancers. Clincopathological data of 338 breast cancer patients were collected, and the association of clinicopathological characteristics with polysomy of chromosome 17 was analyzed. Based on the American Society of Clinical Oncology /College of American Pathologists updated recommendations of HER2 testing in breast cancer in 2013, the relationships between the copy number of centromeres on chromosome 17 (CEP17) and HER2 status, other important biological markers and clincopathological features of breast cancer were analyzed statistically. Immunohistochemical examination revealed that among the 338 breast cancer cases, there were 9 (2.7%) HER2-negative cases, 309 (91.4%) HER2-equivocal cases, and 20 (5.9%) HER2-positive cases. The FISH analysis showed that there were 226 (66.9%) HER2-negative cases, 13 (3.8%) HER2-equivocal cases, and 99 (29.3%) HER2-positive cases. Among the 338 breast cancer patients, 42 (12.4%) cases were identified as chromosome 17 polysomy (polysomy 17), 291 (86.1%) cases were chromosome 17 disomy, and 5 (1.3%) cases were chromosome 17 monosomy. Polysomy 17 showed significant correlation with the intensity of HER2 protein expression (P=0.046). The HER2 FISH results and HER2 gene copy number of polysomy 17 cases showed significant differences from the non-polysomy 17 cases (P<0.001). There were no significant differences of HER2/CEP17 ratio between the polysomy 17 and non-polysomy 17 groups (P=0.930). Polysomy 17 cases showed a significant relationship with tumor grading and Ki-67 index (P<0.05), but not with the age of patient, tumor size, lymph node metastasis, ER and PR expressions, and effect evaluation of neoadjuvant chemotherapy (P>0.05). In the breast cancer with polysomy of chromosome 17, assessment of the absolute copy number of HER2 signals is even more important, and the HER2/CEP17 ratio and HER2 protein expression levels should be comprehensively evaluated together.