Human Epidermal Growth Factor Receptor 2 (HER2) Status Determination Using Single Color Versus Dual Color Fluorescence In-Situ Hybridization(FISH) Assay: Impact of Monosomy and Polysomy 17
LA Niemeier, D Dabbs, U Surti, K Cieply, J Yu, R Bhargava. University of Pittsburgh, Pittsburgh, PA
Background: The CAP/ASCO guideline is an important document for interpretation of HER2 FISH results. A FISH result of more than 6 HER2 gene copies per nucleus (using single color FISH or S-FISH) or HER2 to chromosome 17 ratio of more than 2.2 (using dual color FISH or D-FISH) are considered positive for HER2 gene amplification. An equivocal result is 4-6 copies of HER2 per cell (S-FISH) or ratio of 1.8 to 2.2 (D-FISH). However, CAP/ASCO guidelines fails to address the discordance that can occur based on the type of probe used (S-FISH versus D-FISH) especially when monosomy or polysomy for chromosome 17 is present.
Design: The current study was performed to determine the impact of monosomy and polysomy 17 in the context of S-FISH and D-FISH. Monosomy 17 was defined as one signal for chromosome enumeration probe 17 (CEP17) in >50% of the examined cells. Polysomy 17 was defined as an average of 3 or more signals for CEP17. The monosomy cases were obtained from our partner institution that performed D-FISH on 53 consultation cases. The 20 polysomy cases were obtained from our previously studied dataset (Mod Pathol. 2009;22 (Supplement 1): Abstract 179). All polysomy cases showed 2+ expression by immunohistochemistry. Although the FISH was performed using dual color probe, the data was analyzed based on HER2 gene signal/cell (S-FISH) versus HER2:CEP17 ratio (D-FISH).
|SFISH- Not Amplified||SFISH- Equivocal||SFISH- Amplified|
|DFISH- Not Amplified||30||0||0|
|SFISH- Not Amplified||SFISH-Equivocal||SFISH-Amplified|
|DFISH- Not Amplified||7||10*||3*|