ABSTRACT
OBJECTIVES: Polysomy has been reported in 8 to 68% of invasive breast carcinomas. Polysomy 17 is frequently found in breast cancer and may complicate the interpretation of HER2 testing results. Abnormalities of chromosome 17 can lead to discrepant interpretations of FISH data. This study aimed to review the impact of polysomy 17 on HER2 testing and studied its clinicopathologic significance in relation to HER2 gene amplification and predicted treatment with trastuzumab. MATERIAL AND METHODS: A literature review was performed on polysomy 17 to clarify the significance of chromosome 17 polysomy in invasive breast cancer and show how the increase of CEP17 copy number is currently assessed for novel polysomy 17 testing techniques. CONCLUSIONS: Polysomy 17 tumors cannot be distinguished from HER2-negative tumors by standard pathologic criteria, including tumor grade and hormone receptor status. The literature indicates that HER2-directed therapy does not add benefit to cytotoxic chemotherapy in metastatic HER2 FISH-negative patients with polysomy 17; however, there is still controversy concerning clinical responses to trastuzumab in those specific cases. Accordingly, more studies with chromosome 17 polysomy and FISH negative are required.