Abstract PD10-03: Is 5-50% of Amplified Cells a Suitable Cut Off To Define Heterogeneous Amplification of the HER2 Oncogene?

Abstract

Abstract Background: A recent panel guideline, published on behalf of the College of American Pathologists, redefines heterogeneous amplification of HER2 as the presence of between 5-50% of cells with a HER2/CEP17 ratio ≥2.20[Vance et al., 2009]. We are unaware of pre-existing data auditing either the frequency of cells with this ratio in FISH analysis or of the clinical impact of this definition. Without such data it is difficult for clinicians to interpret the reporting of a breast cancer with 5% HER2 amplified in the context of therapeutic decision making. Patients & Methods: An audit of FISH results from the Birmingham Heartlands Hospital (BHH) routine pathology laboratory was combined with data from analysis of the TEAM pathology study (TPS). All case reports were scanned and the percentage of amplified cells was reported in all cases with at least 20 cells scored as per UK guidelines. Interim data on 1050 cases from Birmingham & 1870 cases from the TEAM trial are reported and the impact of “heterogeneous amplification” on outcome will be presented at the meeting. Results: Cohort 1: BHH: Of 1050 eligible cases 187 (17.8%) were amplified as defined by UK guidelines (HER2/CEP17 ratio ≥2.00). Of these 32 would be defined as “borderline” by the ASCO/CAP guidelines. All cases were referred due to equivocal IHC results (2+ etc). 147 cases exhibited ≥50% of cells with ratios >2.20 “amplified” under the CAP panel guidelines; 51/147 exhibited at least 30% of “non-amplified” cells (ratio <2.20). A further 381 cases (36.2%) exhibited between 5-50% of cells 5-50% of cells with a HER2/CEP17 ratio of greater than 2.20 and would under new CAP guidelines be regarded as exhibiting “Heterogeneous amplification”. Cohort 2 TPS: Of 1870 eligible cases, 220 (11.2%) were amplified for HER2 as defined using conventional parameters of HER2/CEP17 ratios above 2.0(as per UK guidelines). Of these 16 cases would be defined as “borderline” by ASCO/CAP guidelines. All cases were ER+ve accounting for the lower frequency of HER2 amplification. 180 cases (9.6%) exhibited ≥50% of cells with ratios above 2.20 satisfying the new CAP guidelines for amplification (non-heterogeneous). Of these 72 (40%) exhibited at least 30% of cells with ratios <2.20. Conclusion: Using the new CAP panel guidelines for HER2 “heterogeneous amplification” in an audit of 2920 cases identified 955 (32.7%) of heterogeneous amplification, and raised the frequency of “HER2 amplification/heterogeneous amplification” to 44% of cases evaluated. Heterogeneous amplification of the HER2 oncogene is a real and challenging diagnostic finding Evidence relating to the prognostic impact and in particular response to HER2 therapies is currently lacking for these cases. Guidelines should reflect this and seek to gather such evidence before implementing changes to diagnostic practice. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr PD10-03.