Abstract 2384: A new, highly sensitive IHC test for the detection of HER2 protein in breast cancer (BC) tissue.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC HER2 protein over-expression occurs in 15-20% of invasive BC. Trastuzumab and other HER2-targeted agents have mainly been investigated in HER2 over-expressing BC (HercepTest™ 2+/3+). Analysis of clinical study NSABP-31 suggests patients with HER2 non-over-expressed BC (HercepTest™ 0, 1+, 2+ and/or HER2 FISH negative) may benefit from anti-HER2 therapy. Other novel agents are under investigation in HER2 non-over-expressed BC including AZD8931. No IHC assays are optimized for reliable detection of HER2 in the non-over-expressed range. We have therefore developed a highly sensitive, robust HER2 IHC test with a low limit of detection (HER2Low Test). Methods and results: The HER2Low Test uses a novel, high affinity anti-HER2 rabbit monoclonal antibody. Antibody specificity was demonstrated by western blotting using cell lysates expressing HER1, HER2, HER3 or HER4. Analytical sensitivity experiments on BC cell lines showed an ability to differentiate lower levels of HER2 than HercepTest™. Three HER2Low Test staining categories were defined: Low, Medium and High, reflecting differing levels of HER2 expression. A comparative study between HER2Low Test and HercepTest™ on 182 AZD8931 clinical trial BC samples with appropriate ethical approval and consent (Table) showed a redistribution of HercepTest™ scores 0, 1+ and 2+ into HER2Low Test categories Low, Medium and High, demonstrating increased analytical sensitivity of the HER2Low Test. HER2Low Test reproducibility and repeatability studies showed intra-run agreement of 97%, inter-run agreement of 96%, inter-instrument agreement of 87% and observer-to-observer agreement of 89%. Conclusion: Presented here is a novel, reproducible and highly sensitive HER2 IHC assay. This is the first study to demonstrate accurate differentiation across a wide range of HER2 expression levels in non-over-expressed BC. This assay may supplement existing HER2 testing methods for the accurate segmentation of HER2 non-over-expressing BC patients. | | | HER2Low Test | Total | |:----- | ----------------- | ------------ | ---------- | ---------- | | | | Low | Medium | High | | | HcT | | 11 | 34 | 12 | 57 (31.3%) | | | 1+ | 4 | 24 | 36 | 64 (35.2%) | | | 2+ | | 11 | 50 | 61 (33.5%) | | | 3+ (not included) | | | | 0 (0.0%) | | Total | | 15 (8.2%) | 69 (37.9%) | 98 (53.9%) | 182 | HER2Low Test score and conventional HercepTest™ (HcT) score in the tested samples from a phase II clinical trial ([NCT00900627][1]" locator-type="CLINTRIALGOV">[NCT00900627][1]) Citation Format: Hans Christian Pedersen, Anni Thomsen, Kristian Jensen, Karen Jakobsen, Bob Wellings, Gillian Dalgliesh, Kerrie Tosh, Chris Harbron, Jill Walker. A new, highly sensitive IHC test for the detection of HER2 protein in breast cancer (BC) tissue. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2384. doi:10.1158/1538-7445.AM2013-2384 [1]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT00900627&atom=%2Fcanres%2F73%2F8_Supplement%2F2384.atom