Abstract P2-02-03: Circulating tumor cells (CTCs), CTC heterogeneity and distinct morphological CTC subtypes predict worse survival in metastatic breast cancer (MBC)
Authors: O'Shaughnessy Joyce A , Levin Maren K , Rodriguez Esther San Roman , Lu James , Jones Joshua T , Anderson Amanda KL , Tubbs Alisa , Schonhoft Joseph D , Wenstrup Rick 
Published: March 2022

Circulating tumor cells (CTCs), CTC heterogeneity and distinct morphological CTC subtypes predict worse survival in metastatic breast cancer (MBC)BackgroundThe presence of CTCs has been shown to be a poor prognostic factor in patients with MBC. Studies in prostate cancer have shown patients with distinct morphological subtypes of CTCs have worse outcomes than high CTC burden alone and could have treatment implications. In this study, we report a comprehensive analysis of CTC phenotypes in MBC and their impact on survival.MethodsA total of 148 blood samples from 90 patients with MBC whose disease was progressing on therapy were enrolled for CTC analysis. Blood was sent overnight to Epic Sciences, processed onto glass slides and biobanked. Replicate slides were stained with antibodies targeting the androgen receptor (AR), estrogen receptor (ER), and human epidermal growth factor receptor 2 (HER2) in addition to cytokeratin, CD45, and DAPI. Total CTCs were quantified per sample from approximately 3 mL of blood. A threshold defining positive AR, ER, and HER2 protein expression was set using cultured cancer cell lines expressing the individual proteins. CTC morphology subtypes (heterogeneity [Scher et al Cancer Res 2017], small cell/neuroendocrine-like [SC/NE; Brown et al CCR 2021] and chromosomal instability [CIN+; Schonhoft et al Cancer Res 2020]) were quantified as previously described. High heterogeneity samples (Het+) were defined as having a Shannon Index (SI; a measure of morphologic diversity) of ≥1. CIN positivity was defined as having ≥0.7 CIN+ CTC/mL. Association with these CTC subtypes and survival were evaluated with a univariate COX proportional hazard model. ResultsOver 90% of samples and patients had CTCs (Table 1). The percentage of patients with the CTC subtypes evaluated are below. Table 1. Percentage of blood samples with CTCs and CTC subtypes in MBC patients, by MBC subtype

The presence of CTCs was associated with worse survival, with a median survival of 15.3 months (mos) vs 24.0 mos with no CTCs (p=0.028). The presence of AR+ or HER2+ CTCs was not associated with survival. Analysis of ER is ongoing and will be presented. High morphologic heterogeneity or the presence of the SC/NE or CIN+ CTC subtypes, predicted for a worse survival outcome (Table 2). Table 2. Overall survival of patients with and without distinct CTC subtypes

CTC morphological subtypes did not correlate with each other, except CTC heterogeneity by SI which correlated weakly with SC/NE and CIN+. HER2+ CTCs strongly correlated with a higher SI while AR+ CTCs did not. AR and HER2 expression did not associate with the CIN+ or SC/NE subtypes. ConclusionsDigital pathology analysis of CTCs identifies distinct CTC morphological subtypes that predict for worse prognosis in MBC patients. To our knowledge, this is the first report of SC/NE CTCs in MBC patients and that MBC patients with SC/NE and CIN+ CTCs have worse outcomes. Longitudinal characterization of CTC subtypes across the MBC continuum could potentially identify effective therapies against these more lethal cancers.

Citation Format: Joyce A O'Shaughnessy, Maren K Levin, Esther San Roman Rodriguez, James Lu, Joshua T Jones, Amanda KL Anderson, Alisa Tubbs, Joseph D Schonhoft, Rick Wenstrup. Circulating tumor cells (CTCs), CTC heterogeneity and distinct morphological CTC subtypes predict worse survival in metastatic breast cancer (MBC) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-02-03.