HER2/Neu Gene Amplification Heterogeneity: The Significance of Cells with a 3:1 HER2/CEP17 Ratio
Lester J Layfield, Robert Schmidt. University of Utah School of Medicine, Salt Lake City, UT; ARUP Laboratories, Salt Lake City, UT
Background: The CAP produced guidelines for HER2 amplification heterogeneity. Heterogeneous populations may behave differently than homogeneous populations. When 20 cells are counted to evaluate HER2/neu amplification, a single 3:1 HER2/CEP17 ratio cell characterizes the sample as heterogeneous non-amplified. Such heterogeneous cases may behave differently than heterogeneous non-amplified cases secondary to multiple cells with ratios>2.20 or cases with a single cell having a ratio>3:1. Heterogeneity may indicate biologically important characteristics.
Design: Fluorescence in situ hybridization was performed for each of 1547 cases and 20 cells of invasive carcinoma were analyzed for HER2/CEP17 ratio. Cases were assessed as non-amplified (ratio<1.8), borderline amplified (ratio of 1.8 to 2.2) or amplified (ratio>2.20). Heterogeneity was present when the percentage of cells with ratios above 2.20 was ≥5% but <50%. Individual cells were typed by probe ratios. The distribution of HER2/CEP17 ratio was determined with the number of 3:1 HER2/CEP17 cells plotted against the number of amplified cells. The probability of a heterogeneous population being present was plotted against the number of 3:1 cells in the sample.
Results: 3:1 HER2/CEP17 ratio cells occur with low frequency (2.2%) but are the determining factor for heterogeneity in 46% of heterogeneous cases. Thirty five percent of heterogenous cases were due to a single 3:1 cell. A single 3:1 cell in a sample is a poor predictor of additional amplified cells. Among cases with a single 3:1 cell, only 30% contain an additional amplified cell. 3:1 ratio cells were responsible for 10% of the diagnoses of amplification. 3:1 cells were not associated with heterogeneity in amplified cases (p<0.36) but were associated with heterogeneity in borderline cases (p<0.002).
Conclusions: Our data suggests that inclusion of cells with a 3:1 HER2/CEP17 ratio in the definition of heterogeneity may be too broad as these cells are a determining factor in approximately one-third of diagnoses of heterogeneity but are not strongly associated with other measures of amplification. 3:1 ratio cells are a poor predictor for the presence of additional amplified cells in a sample. The lower cut point for heterogeneity is in a region sensitive to error. A small counting error may result in a diagnosis of heterogeneity. The importance of small numbers of 3:1 HER2/CEP17 ratio cells in a sample should be reassessed as they may not reflect a poor prognosis or the likelihood of amplified cells in metastases.
Wednesday, March 21, 2012 9:30 AM
Poster Session V # 51, Wednesday Morning