Decoding Cancer's Cloaking Device: New Insights into Circulating Tumor Cells
"Unlocking the Secrets of CTC Heterogeneity for Personalized Cancer Treatment"
Metastasis, the spread of cancer from its primary site, remains the leading cause of cancer-related deaths. This complex process involves the release of circulating tumor cells (CTCs) into the bloodstream, acting as seeds for new tumors in distant organs. Understanding CTCs is crucial for developing strategies to prevent and treat metastasis.
Liquid biopsies, which analyze CTCs in blood samples, have emerged as a promising tool for cancer diagnosis, monitoring, and treatment planning. However, current methods often rely on detecting specific markers, like EPCAM, on the surface of CTCs. This approach overlooks the fact that CTCs can be highly diverse, with some shedding or reducing these markers as they undergo epithelial-mesenchymal transition (EMT), a process that allows them to become more mobile and invasive.
A recent study published in Biomarker Research introduces a novel approach to identify and characterize CTCs, regardless of their EPCAM expression. By using patient-derived xenografts (PDXs) – models where patient tumor cells are grown in mice – and a highly sensitive human-specific qRT-PCR assay, researchers were able to quantify CTCs and analyze their gene expression profiles, offering new insights into CTC heterogeneity and potential therapeutic targets.
CTCs in Liquid Biopsy
Circulating tumor cells (CTCs) are cancer cells shed from primary or metastatic tumors into the bloodstream. Their rarity—estimated at about one CTC per billion blood cells—has been a major technical barrier to studying them. Blood-based detection of cancer cells and other tumor-associated products is described as liquid biopsy, and CTC analysis can offer insight into metastasis, tumor-genotype changes during treatment, and treatment resistance.
Broadening the Meaning of Liquid Biopsy
Liquid biopsy is now commonly associated with blood and the circulating biomarkers that can be extracted from it, but other fluids from the body can also provide circulating cells, DNA, or other biomarkers. Research on liquid biopsy has prominently focused on circulating tumor DNA, circulating tumor cells, and exosomes. A recent historical review describes a shift in ctDNA analysis from targeted approaches toward genome-wide analysis.
Beyond EPCAM: A New Strategy for CTC Detection
The limitations of current CTC detection methods, which primarily rely on the presence of epithelial markers like EPCAM, have prompted researchers to seek alternative approaches. The study in Biomarker Research tackles this challenge by employing patient-derived xenografts (PDXs). These models allow for the study of human CTCs in a murine genetic background, minimizing contamination from normal human cells.
- Unbiased Detection: It identifies CTCs irrespective of EPCAM expression, capturing a wider spectrum of tumor cells.
- High Sensitivity: The qRT-PCR assay allows for the detection of rare human transcripts in the murine background.
- Heterogeneity Analysis: The method enables the characterization of gene expression profiles in CTCs, providing insights into their diverse nature.
Immune Evasion and CTC Diversity
A 2024 review reports that CTCs can secrete the immunosuppressive factors TGF-β and IL-10, which may inhibit immune-cell activation and function and create an environment that shields CTCs from immune attack. CTCs are not all alike in their surface-marker expression: studies using EpCAM-independent detection methods have found that both EpCAM-positive and EpCAM-negative tumor cells can circulate in blood. This diversity can complicate the molecular characterization of cells expanded from CTCs, because their prior phenotypic heterogeneity may affect the results.
Limits of Liquid Biopsy Evidence
Liquid biopsy is a minimally invasive way to examine tumor-derived material, including CTCs and circulating tumor DNA, in blood or other body fluids. However, current CTC detection has limitations in both specificity and sensitivity, which should be considered when interpreting published findings. A 2025 umbrella review aims to map and evaluate the evidence for liquid biopsy across medical specialties and conditions, underscoring that its support must be assessed across different uses.
Implications for Personalized Cancer Therapy
The findings of this study have significant implications for personalized cancer therapy. By identifying and characterizing CTCs independently of EPCAM expression, clinicians can gain a more complete understanding of the metastatic potential of a patient's tumor. This, in turn, can lead to more informed treatment decisions and the development of targeted therapies that address the specific characteristics of a patient's CTCs.
Metastasis and the Value of CTC Research
Cancer remains a leading cause of mortality worldwide, and metastasis contributes significantly to its lethality. Because tumor cells can spread primarily through the bloodstream, circulating tumor cells are an important focus of oncology research. The cited review describes CTCs as a component of liquid biopsy that can provide a non-invasive, dynamic window into tumor biology.
Promise and Path to Clinical Use
Recent work discusses liquid biopsy, including CTC analysis, in relation to cancer screening, early detection of relapse, real-time monitoring of treatment efficacy, and identifying therapeutic targets and resistance mechanisms. A 2024 review focused on CTCs also examines current clinical implications and the hurdles that must be addressed before liquid biopsy can be incorporated into standard-of-care guidelines. A 2026 article describes liquid biopsy as a promising approach for detecting cancers through analysis of tumor-derived components circulating in blood, including CTCs.
The researchers propose that their approach could be used to identify novel CTC markers, which could then be used to develop new capture and detection methods. This would allow for the isolation and characterization of viable, heterogeneous CTCs, providing a valuable resource for drug development and personalized medicine.
While this study focuses on breast cancer PDX models, the approach can be extended to other cancer types. The ability to comprehensively analyze CTCs, regardless of their epithelial marker expression, holds great promise for improving cancer diagnosis, monitoring, and treatment, ultimately leading to better outcomes for patients.