How does aneuploidy of chromosome 17 affect the results of HER2 tests of breast tumors?

Updated: Mar 20, 2019
  • Author: Oudai Hassan, MD; Chief Editor: Chandandeep Nagi, MD  more...
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Answer

Aneuploidy of chromosome 17

Polysomy 17 is seen in approximately 8% of all specimens, mostly among cases with 4-6 HER2 gene copies; these were previously labeled as equivocal. If polysomy 17 is defined as three or more CEP17 copies, most are not associated with mRNA overexpression. Most tumors with a HER2 gene copy number between 4 and 6 are also not associated with protein mRNA overexpression.

For tumors that are heterogeneous for HER2 amplification on in situ hybridization (1-2% of cases), the maximal HER2 values should be reported with a note that the tumor demonstrated heterogeneity for HER2 amplification. [20]


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