polysomy 17

Tumors

 mammary carcinomas (breast cancer)

• HER2 gene amplification by fluorescence in situ hybridization and protein expression by immunohistochemistry (IHC) have been used for prognosis and guiding treatment of invasive ductal carcinoma of the breast with trastuzumab.
• Accurate evaluation of HER2 status is important in the management of patients with candidacy for the HER2-targeting therapy.
• Despite previous studies, effects of polysomy of chromosome 17, at which HER2 is located, on HER2 protein expression remains controversial.
• In conclusion, a high HER2 gene copy number-associated polysomy 17 is a significant contributing factor in HER2 protein overexpression in unamplified invasive breast carcinomas.
• Cases without HER2 amplification, but carrying polysomy 17, should be further evaluated for HER2 protein overexpression by IHC.
• Those with polysomy 17-associated HER2 protein overexpression, like any other IHC+ ones, should be eligible candidates for trastuzumab therapy.

References

 Effect of high copy number of HER2 associated with polysomy 17 on HER2 protein expression in invasive breast carcinoma. Shah SS, Wang Y, Tull J, Zhang S. Diagn Mol Pathol. 2009 Mar;18(1):30-3. PMID: 19214111