Abstract 4459: Morphologic and genomic characterization of circulating tumor cells in patients with ERBB2 mutant HER2 non-amplified metastatic breast cancer treated with neratinib

Abstract

Abstract Metastatic breast cancer patients have a high risk of progression and face poor prognosis overall, with about one third (34%) surviving 5 years or more. In rare instances (2-4% of cases) patients with metastatic breast cancer have ERBB2 (HER2) activating mutations, but are HER2 negative (non-amplified. Neratinib is a potent, irreversible inhibitor that binds HER2 and inhibits downstream signaling. We used the previously validated high-definition single cell analysis (HD-SCA) workflow to investigate the clinical significance of circulating tumor cells (HD-CTCs) in HER2-mutant, HER2 non-amplified, post-menopausal metastatic breast cancer patients starting neratinib and fulvestrant combinational therapy. Genomic analysis of the cell-free DNA (cfDNA) and single cell HD-CTCs was conducted to monitor tumor evolution and identify potential mutational variants unique to the patient’s clinical response. A subset of 5 patients presented here were from the MutHER (NCT01670877) and/or SUMMIT (NCT01953926) trials. Patients had an average of 5.4 lines of therapy before enrollment, variable hormone receptor status, and ERBB2 mutations at diagnosis and during treatment. HD-CTC enumeration alone was not sufficient to predict clinical response. Interestingly, treatment pressure was shown to lead to an observable change in HD-CTC morphology and genomic instability, suggesting these parameters may inform prognosis. Single cell copy number variation (CNV) analysis indicated that the persistence or development of a clonal population of HD-CTCs during treatment was associated with a worse response. Hierarchical clustering analysis of the single cells across all patients and timepoints identified distinct aberrant regions shared among patients, comprised of 26 genes that are similarly affected and may be related to drug resistance. Additionally at the cfDNA level, we identified new mutations in ERBB2, PIK3CA, and TP53 that arose due to treatment pressure in a patient with poor response, further informing us on the dynamics of the cancer genome over the course of therapy. The data presented in this small cohort study demonstrates the feasibility of real-time molecular profiling of the cellular and acellular fractions of the liquid biopsy using the HD-SCA platform. Additional insight is warranted to determine the potential use of morphometric and genomic analysis as a prognostic tool to advance personalized oncology. Citation Format: Stephanie Nicole Shishido, Rahul Masson, Lisa Welter, Liya Xu, Anishka D'Souza, Darcy Spicer, James Hicks, Janice Lu, Peter Kuhn. Morphologic and genomic characterization of circulating tumor cells in patients with ERBB2 mutant HER2 non-amplified metastatic breast cancer treated with neratinib [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4459.