Single HER2-positive tumor cells are detected in initially HER2-negative breast carcinomas using the DEPArray™-HER2-FISH workflow

Real-time assessment of HER2 status in circulating tumor cells of breast cancer patients: Methods of detection and clinical implications

The human epidermal growth factor receptor 2 (HER2) plays a central role in breast cancer (BC). Therefore, it is critical to develop a method that can capture its spatial and temporal heterogeneity. Nowadays, therapeutic decisions for BC patients relies on evaluation of HER2 status from tissue biopsies using immunohistochemistry and in situ hybridization. Nevertheless, considering the technical and logistical challenges associated with tissue biopsies, there is an unmet need for a non-invasive and accurate approach to obtain real-time assessment of HER2 status. In this context, circulating biomarkers, particularly circulating tumor cells (CTCs), emerged as promising candidates. HER2 assessment on CTCs can be performed at genomic, transcriptomic, and protein levels on both bulk CTCs and at the single-cell resolution. However, the main limitation of the literature to date is the lack of a consistent definition of HER2-positive CTCs, which poses a major challenge for both, future research and clinical applications. Several studies revealed discordance in HER2 status between the primary tumor and corresponding CTCs. For instance, HER2-positive CTCs have been detected among patients with HER2-negative BC and vice versa. As a result, researchers have evaluated the prognostic and predictive value of HER2 status in CTCs, both in the early and metastatic settings, to increase the possibility of using anti-HER2 therapy also for these patients and to dissect mechanisms of treatment resistance. This review aims to provide an overview of the methods to determine HER2 status in CTCs and to summarize the evidence and future perspective on how CTCs-HER2 assessment can be integrated into the clinical management of BC patients.

The Diversity of Liquid Biopsies and Their Potential in Breast Cancer Management

Analyzing blood as a so-called liquid biopsy in breast cancer (BC) patients has the potential to adapt therapy management. Circulating tumor cells (CTCs), extracellular vesicles (EVs), cell-free DNA (cfDNA) and other blood components mirror the tumoral heterogeneity and could support a range of clinical decisions. Multi-cancer early detection tests utilizing blood are advancing but are not part of any clinical routine yet. Liquid biopsy analysis in the course of neoadjuvant therapy has potential for therapy (de)escalation.Minimal residual disease detection via serial cfDNA analysis is currently on its way. The prognostic value of blood analytes in early and metastatic BC is undisputable, but the value of these prognostic biomarkers for clinical management is controversial. An interventional trial confirmed a significant outcome benefit when therapy was changed in case of newly emerging cfDNA mutations under treatment and thus showed the clinical utility of cfDNA analysis for therapy monitoring. The analysis of PIK3CA or ESR1 variants in plasma of metastatic BC patients to prescribe targeted therapy with alpesilib or elacestrant has already arrived in clinical practice with FDA-approved tests available and is recommended by ASCO. The translation of more liquid biopsy applications into clinical practice is still pending due to a lack of knowledge of the analytes' biology, lack of standards and difficulties in proving clinical utility.

Detection of Circulating Tumor Cells in Cerebrospinal Fluid of Patients with Suspected Breast Cancer Leptomeningeal Metastases: A Prospective Study

BACKGROUND

The diagnosis of breast cancer (BC)-related leptomeningeal metastases (LM) relies on the detection of tumor cells in cerebrospinal fluid (CSF) using conventional cytology (gold standard). However, the sensitivity of this technique is low. Our goal was to evaluate whether circulating tumor cell (CTC) detection in CSF using the CellSearch® system could be used for LM diagnosis.

METHODS

This prospective, monocentric study included adult patients with suspected BC-related LM. The clinical sensitivity and specificity of CTC detection in CSF for LM diagnosis were calculated relative to conventional CSF cytology.

RESULTS

Forty-nine eligible patients were included and 40 were evaluable (CTC detection technical failure: n = 8, eligibility criteria failure: n = 1). Cytology was positive in 18/40 patients. CTCs were detected in these 18 patients (median: 5824 CTC, range: 93 to 45052) and in 5/22 patients with negative cytology (median: 2 CTC, range: 1 to 44). The detection of ≥1 CSF CTC was associated with a clinical sensitivity of 100% (95% CI, 82.4-100) and a specificity of 77.3% (95% CI, 64.3-90.3) for LM diagnosis. HER2+ CTCs were detected in the CSF of 40.6% of patients with HER2- BC (median: 500 CTC, range: 13 to 28 320).

CONCLUSIONS

The clinical sensitivity of CTC detection in CSF with the CellSearch® system for LM diagnosis is higher than that of CSF cytology. CTC detection in patients with negative cytology, however, must be further investigated. The finding of HER2+ CTCs in patients with HER2- BC suggests that the HER2 status of LM should be evaluated to increase the treatment opportunities for these patients.