Abstract LB-112: A retrospective study to assess the potential for the TheraLink® HER family assay, a reverse-phase protein microarray assay, to predict treatment benefit in breast cancer

Abstract

Abstract Background A significant percentage of patients with HER2+ breast cancer exhibit de novo resistance or develop an acquired resistance to anti-HER therapy. HER2 overexpression is currently used to guide anti-HER2 therapy by either IHC to measure the total amount of HER2 protein present, or FISH to measure the number of copies of the HER2 gene. Several potential mechanisms for this resistance have been proposed, ranging from mechanisms intrinsic to the target itself to the involvement of compensatory signaling pathways. As current therapy-guiding assays provide a measure of the level of HER2 protein, a better predictor of response may be possible through an assessment of not only HER2 activation (phosphorylation status), but also the protein levels of the other HER family members, their activation, and the activation of downstream resistance signaling pathways. To provide evidence that HER receptors are actively signaling, and to identify alternative therapies, a measure of the activation status of key signal transduction pathways downstream of these receptors was performed. The availability of molecular diagnostic assays that can evaluate phosphoproteins is an appealing approach to predicting treatment-sensitivity and to select more effective therapies. Methods De-identified breast tissue samples, including a subset of samples having their HER2 status identified by IHC and FISH were received for phosphoproteomic analysis using the TheraLink® HER Family Assay. The assay utilizes reverse-phase protein microarray (RPMA) to measure the total protein level and activation status of multiple proteins directly from a FFPE-biopsy lysate. The TheraLink® Assay measures the protein levels of EGFR, HER2, and HER3, their phosphorylation status, and the activation status of proteins in three downstream signaling pathways: AKT/mTOR; Mek/Erk; and Jak/STAT. Results The TheraLink® Assay's panel identified the cohort of tumors with known HER2 status (100% concordance between HER2 level measured by RPMA platform and IHC/FISH). Moreover, unsupervised clustering of this subset of samples identified three patterns of unique signaling. The first group showed high phosphorylation levels of HER2 and EGFR protein, suggesting the potential use of a dual kinase inhibitor therapy. The PI3 kinase and MAPK pathways were also elevated in this cohort. A second group that might not benefit from mono-therapy was observed. This group showed high levels of HER3 protein, a well-known dimerization partner for HER2. Therefore, this group might benefit from an anti-dimerization therapy, like pertuzumab. The PI3 Kinase and Jak/Stat pathways were also highly activated in this cohort. A third unique group exhibiting only activation of HER2 and HER3 was observed, with no downstream activity. Although a pan-HER kinase inhibitor has therapeutic potential, further downstream pathways, as well as other tyrosine kinase receptors, should be further examined. Conclusion The TheraLink® Assay has the potential to identify therapeutic strategies that might provide benefit to patients that are HER2 positive but failing on anti-HER2 therapy. Alternative therapeutics can be more precisely identified using the TheraLinkTM HER Family Assay's panel, based upon the molecular uniqueness of the groups described. Citation Format: Corinne Ramos, Nicholas Hoke, George J. Snipes, Pinar Yurt, Cody Thomas, Tuan Tran. A retrospective study to assess the potential for the TheraLink® HER family assay, a reverse-phase protein microarray assay, to predict treatment benefit in breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-112. doi:10.1158/1538-7445.AM2015-LB-112