Identifying Molecular Targets And Mechanisms Of Treatment Resistance In Inflammatory Breast Cancer (Ibc) Using Reverse-Phase Protein Microarrays (Rpma)

Background Inflammatory Breast Cancer (IBC) is a clinicopathologic diagnosis characterized by rapid progression and poor prognosis. Even with the advent of targeted therapies and a multimodal approach, IBC is often treatment refractory and a therapeutic challenge for all subtypes, including ER+ and HER-2 amplified (HER2+) disease (Masuda et al). Therefore identifying mechanisms of resistance to molecularly targeted therapy could provide clues to improve management and outcome. Recent studies comparing the gene expression profiles of IBC tumors with non-IBC demonstrated that HER2+ IBC have increased mTOR signaling compared to their non-IBC counterparts (Iwamoto et al). mTOR activation is a mechanism for Trastuzumab resistance and may contribute to treatment resistance in HER2+ IBC. The availability of molecular diagnostics evaluating phosphoproteins is an appealing approach to predict treatment-sensitivity and select more effective combinations. Methods This is an observational analysis of 12 IBC patients who had tissue biopsy after progression on standard therapies including HER-2 targeted therapies. Tissue analysis for expression of cancer-related phosphoproteins was performed using TheraLink™. The TheraLink™ assay uses reverse-phase protein microarrays (RPMA) to quantify HER1, HER2, and HER3 receptor overexpression; it also evaluates for phosphorylation of the receptor which indicates activation. Phosphorylation of HER downstream signaling pathways such as JAK2, AKT/mTOR and MEK1/2 are also detected. Additionally, next generation sequencing (NGS) using FoundationOne™ was performed if sufficient tissue was available. Results All patients had IBC and most had metastatic disease (83%). According to subtype 25% of patients were ER+/HER2-, 42% ER+/HER2+, 25% ER-/HER2+, 8% ER-/HER2-. 58% of tumors demonstrated HER1 activation, 75% had HER2 activation and 58% had HER3 activation. Interestingly, 83% had mTOR activation, and most of these patients also had accumulation of its downstream proteins, S6 ribosomal protein and 4E-BP-1. 78% of patients with HER2 activation also had mTOR activation. Two of the 4 patients who were HER2- by IHC/FISH had HER2 activation by RPMA. Six patients also had NGS on tissue; 75% had concordance between HER2 activation on TheraLink™ and ERBB2 amplification on NGS, 67% had concordance with mTOR activation on TheraLink™ and mutation in the mTOR pathway (PIK3CA mutation or PTEN loss) on NGS. One patient with triple negative, chemo-refractory IBC who underwent 3 lines of neoadjuvant therapy prior to bilateral mastectomy was found to have HER1, HER2, HER3 and mTOR activation; she was started on lapatinib and capecitabine and remains with no recurrent disease and on treatment. Conclusions Patients with IBC often have activation of members of the HER family and mTOR pathway indicating molecular targets and potential mechanisms of resistance in IBC. The concomitant use of NGS and RPMA is an intriguing approach to molecular diagnostics in this aggressive and treatment refractory disease providing additional information on pathway activation leading to expanded therapeutic options. Future prospective studies should clarify the potential impact in treatment selection and outcome. Citation Format: Laura Austin, Kimberly Limentani, Juan Palazzo, Tiffany Avery, Rebecca Jaslow, Ron Hencin, Emanuel F Petricoin, Massimo Cristofanilli. Identifying molecular targets and mechanisms of treatment resistance in inflammatory breast cancer (IBC) using reverse-phase protein microarrays (RPMA) [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P2-04-02.