Circulating Tumor DNA in the Management of Early-Stage Breast Cancer

Abstract

Liquid biopsies refer to the isolation and analysis of tumor-derived biological material from body fluids, most commonly blood, in order to provide clinically valuable information for the management of cancer patients. Their non-invasive nature allows to overcome the limitations of tissue biopsy and complement the latter in guiding therapeutic decision-making. In the past years, several studies have demonstrated that circulating tumor DNA (ctDNA) detection can be used in the clinical setting to improve patient prognosis and monitor therapy response, especially in metastatic cancers. With the advent of significant technological advances in assay development, ctDNA can now be accurately and reliably identified in early-stage cancers despite its low levels in the bloodstream. In this review, we discuss the most important studies that highlight the potential clinical utility of ctDNA in early-stage breast cancer focusing on early diagnosis, detection of minimal residual disease and prediction of metastatic relapse. We also offer a concise description of the most sensitive techniques that are deemed appropriate for ctDNA detection in early-stage cancer and we examine their advantages and disadvantages, as they have been employed in various studies. Finally, we discuss future perspectives on how ctDNA could be better integrated into the everyday oncology practice.

Keywords: circulating free DNA; circulating tumor DNA; digital PCR; early-stage breast cancer; liquid biopsies; minimal residual disease; next-generation sequencing; patient surveillance; prognosis; therapy monitoring.

Figure 1

(a) Blood is the most commonly used body fluid for liquid biopsies. The most studied liquid biopsy biomarkers are depicted, namely circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), cell-free RNA (cfRNA), extracellular vesicles (EVs) and tumor-educated platelets (TEPs). Cell-free DNA (cfDNA) is also shown. (b) ctDNA carries the same genomic (point mutations, insertions/deletions, translocations, copy number variations) and epigenomic (DNA methylation) alterations as the tissue tumor DNA. This image was created with the use of BioRender (https://biorender.com/) (accessed on 20 April 2023).

Figure 2

Highly sensitive molecular techniques for ctDNA detection and characterization. Droplet digital PCR (ddPCR) is based on the partitioning of the sample into millions of water-in-oil droplets, so that each droplet contains a single DNA molecule that is amplified individually. BEAMing stands for beads, emulsion, amplification, and magnetics and is a type of dPCR, where amplified wild-type and mutant alleles are differentially labeled and are separated through flow cytometry. Next-generation sequencing (NGS) approaches that employ massive parallel sequencing with improved technical and bioinformatics protocols to reduce errors have gained ground in ctDNA analysis. This image was created with the use of BioRender (https://biorender.com/) (accessed on 20 April 2023).

Figure 3

Analysis of ctDNA at various time points can contribute to the clinical management of early-stage breast cancer (BC). Early diagnosis by ctDNA detection could be followed by administration of neoadjuvant therapy (NAT), and ctDNA testing in post-surgical samples could help in the detection of minimal residual disease (MRD). Longitudinal ctDNA analysis in patients after NAT and/or adjuvant therapy (AT) could also be used in monitoring therapy response, early detection of resistance and prediction of metastatic relapse. This image was created with the use of BioRender (https://biorender.com/) (accessed on 22 April 2023).