[96] Intra-Tumoral Heterogeneity for HER2 Gene Amplification Is Common Using the CAP Recommended Criteria and Does Not Correlate with High Protein Expression: Time for a New Look at How To Report Heterogeneity.

Kimberly H Allison, Suzanne M Dintzis, Rodney A Schmidt. University of Washington Medical Center, Seattle

Background: The College of American Pathologists (CAP) recently published recommendations for reporting intra-tumoral heterogeneity for HER2 gene amplification in breast cancers. These guidelines recommend reporting cases with between 5-50% of cells with HER2:CEP17 ratios > 2.2 as “heterogeneous for HER2 gene amplification.” We examined the implications of applying these recommendations to clinical practice and reviewed the HER2 protein expression by immunohistochemistry (IHC) in the cases with FISH heterogenous results to determine if these criteria are likely to identify additional cases with protein over-expression.
Design: We collected HER2 and CEP17 counts in 32,116 tumor cells from 1329 consecutive breast cancer cases analyzed by FISH at UWMC. Data from Excel counting sheets were imported to a SQL Server database for analysis and statistics. Cases were categorized as CAP heterogenous if between 5-50% of cells counted had HER2:CEP17 ratios > 2.2. These results were then compared with the original FISH CAP/ASCO ratio criteria. Concurrent HER2 IHC results for CAP heterogeneous cases were also pulled from the database for review.
Results: 313 of 1,329 cases (23%) met the proposed CAP criteria for heterogeneous HER2 gene amplification by HER2:CEP17 ratio. Of these cases, 80% were considered non-amplified by the traditional criteria. The below table shows the classification of all cases by both criteria. Of the 284 heterogeneous cases available for IHC review, only 1% were positive for protein over-expression by IHC and the majority were either IHC equivocal (51%) or IHC negative (48%) for HER2 protein over-expression.

Original Classification vs Classification by CAP Heterogeneity Reporting Recommendation

Original Classification by Ratio	Classification by CAP Heterogeneity Recommendation
	Amplified (>50% cells > 2.2)	Heterogeneous (5-50% > 2.2)	Not Amplified (<5% > 2.2)
Amplified	178	12	0
Equivocal	2	49	2
Not Amplified	0	252	834

Conclusions: A significant proportion of breast cancers contain HER2 heterogeneity based on CAP reporting recommendations. The majority of heterogeneous cases were non-amplified by the original classification system and do not over-express HER2 by IHC, bringing into question if the threshold for these reporting recommendations is too low (at 5% of cells) to be clinically relevant. Additional data-driven evidence is needed to determine the most clinically relevant schemes for reporting the common finding of HER2 heterogeneity.
Category: Breast

Monday, February 28, 2011 8:45 AM

Platform Session: Section C, Monday Morning