Abstract P4-01-09: Phenotypic profiling of circulating tumor cells (CTCs) in patients with metastatic breast cancer reveals clinically-relevant heterogeneity in CTC morphology and marker expression

Background: The choice between hormonal therapies and chemotherapy is a frequent decision in the standard of care of metastatic breast cancer (mBCa) patients. We previously developed quantitative measures of phenotypic CTC heterogeneity in metastatic prostate cancer and found that higher heterogeneity was associated with better survival on chemotherapy vs. targeted hormonal therapies in a risk adjusted analysis (Scher et al. 2017 Cancer Research). Here we sought to test the feasibility of measuring CTC heterogeneity in mBCa patients. Methods: 295 blood samples from 165 pts (84 HR+, 19 Her2+, 8 HR+/Her2+, 54 TNBC) from mBCa patients were processed for CTC analysis utilizing the Epic Sciences Functional Cell Profiling platform. Following enumeration, multi-dimensional phenotypic characterization analysis was performed utilizing protein expression and digital pathology features. Features from each CTC (3994 CTCs from 165 pts, were compared by unsupervised clustering to assess intra-patient CTC heterogeneity among mBCa CTC phenotypes. Results: CTCs were detected in 76.9% (227/295) of mBCa patients (med=2.4 CTC/mL, Range 0 - 747). Phenotypic profiling identified distinct CTC subtypes characterized by morphological and protein expression features that correlated with mBCa subtypes. Prevalent CTC features that associated with mBCa were either high cytokeratin (CK) expression or lower nuclear to cytoplasmic (N/C) ratio with lower CK expression. Analysis of mBCa subtypes showed that TNBC pts were characterized by CTCs with a large nuclear area and high CK expression. We observed marked differences in CTC heterogeneity across patients, with some patients having more uniform CTC profiles, and others having higher phenotypic diversity. mBCa subtypes had similar intra-patient heterogeneity level. Conclusions: Distinct CTC phenotypes can be visualized and quantified across patients and associated with specific mBCa subtypes. Our analysis revealed significant heterogeneity between individual CTCs both between and within patients. Identification of patients with high heterogeneity may help to identify patients unlikely to respond to targeted therapies. Studies to link heterogeneity to efficacy of specific therapies and patient outcome are ongoing. Citation Format: Tiziano Pramparo, Adam Jendrisak, Priscilla Ontiveros, Megan Kearney, Lincy Chu, Nadia Ebrahim, Joseph Schonhoft, Rick Wenstrup, Yipeng Wang. Phenotypic profiling of circulating tumor cells (CTCs) in patients with metastatic breast cancer reveals clinically-relevant heterogeneity in CTC morphology and marker expression [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-01-09.