Modern oncology increasingly relies on the integration of anatomical, histopathological, and molecular data. A profound understanding of tumor biological features is a critical prerequisite for treatment personalization, therapeutic response assessment, and disease progression monitoring. In this process, liquid biopsy attracts special attention—a minimally invasive approach that enables the examination of tumor-associated material in biological fluids.
Tissue biopsy remains the fundamental method for morphological diagnosis and many molecular analyses of tumors. However, it reflects a sample obtained from a specific location at a specific moment in time. Especially in metastatic disease, genomic differences between various tumor sites and clones—tumor heterogeneity—can complicate treatment selection. Furthermore, obtaining tissue is sometimes technically difficult, clinically risky, or impossible.
Liquid biopsy offers an opportunity to partially overcome these limitations. One of its most significant directions is the analysis of circulating tumor DNA (ctDNA), which occupies an increasingly important role in the development of precision oncology.
However, when evaluating the capabilities of this technology, the main question is not merely whether we can detect tumor-derived DNA earlier. Equally important is whether this information alters clinical decisions and ultimately improves patient outcomes.
What are liquid biopsy, cfDNA, and ctDNA?
Liquid biopsy is a method of examining tumor-associated material in biological fluids. Blood plasma is most commonly used for analysis, although other biological fluids may be utilized depending on the specific clinical goal and tumor type.
Within the framework of liquid biopsy, various biomarkers can be evaluated, including:
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Cell-free DNA (cfDNA);
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Circulating tumor DNA (ctDNA);
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Circulating tumor cells.
cfDNA consists of DNA fragments present in the extracellular space, including blood plasma, released as a result of cellular processes such as apoptosis and necrosis. ctDNA represents the fraction of cfDNA originating from tumor cells.
ctDNA may contain tumor-associated genomic alterations, including single nucleotide variants, small insertions and deletions, copy number variations, and certain structural rearrangements. Their detection depends on the assay technology used, analytical sensitivity, and the specific type of alteration.
The quantity and detectability of ctDNA are influenced by the tumor type, disease stage, tumor burden, anatomical location, biological features of tumor foci, and treatment effects. Consequently, not all tumors release the same amount of ctDNA into the blood.
Plasma analysis may provide information about DNA released from multiple tumor sites and identify genomic alterations that were not present in a single tissue sample. Nevertheless, it cannot ensure the detection of all tumor clones and clinically significant alterations.
Main Approaches to ctDNA Testing
There are two primary approaches in ctDNA testing.
Tumor-informed assays – initially analyze the genomic features of the patient’s tumor tissue. Then, they search the plasma specifically for selected, tumor-specific alterations. This approach is particularly important in molecular residual disease monitoring studies.
Plasma-only assays – used to detect genetic alterations in blood plasma without prior genomic profiling of the tumor tissue. Their advantage is that they may be useful when tissue samples are unavailable, insufficient, or when tissue-based testing results cannot be obtained within a clinically relevant timeframe.
The choice between these approaches depends on the clinical question, the validated characteristics of the assay, and the decisions the physician plans to make based on the results. A negative or non-informative result from plasma-based tests does not always rule out the presence of a target genetic alteration; in such cases, depending on the clinical situation, tissue testing may be required.
Clinical Application: From Genomic Profiling to Molecular Monitoring
1. Treatment Selection and Evaluation of Therapeutic Resistance
One of the most important clinical applications of ctDNA is identifying actionable genomic alterations for treatment in advanced malignant disease.
In certain tumors, when there is an appropriate biomarker indication and an approved therapeutic option, plasma-based genomic profiling can facilitate the selection of targeted therapy. This is particularly crucial when conducting a tissue biopsy is impossible or associated with significant risk.
During treatment, changes in the molecular profile of ctDNA can provide additional information regarding tumor evolution and resistance-related alterations. However, the clinical interpretation of these changes must be based on the capabilities of the specific assay, tumor type, treatment regimen, and other clinical data.
Importantly, the dynamics of ctDNA concentration or individual molecular alterations should not be independently considered as definitive evidence of treatment response or disease progression.
2. Molecular Residual Disease and Relapse Risk Assessment
One of the most promising directions of liquid biopsy is the assessment of molecular residual disease (MRD).
MRD involves detecting molecular signs of the disease remaining after treatment when standard clinical or radiological methods fail to detect it.
Following radical surgical intervention or other curative-intent treatments, the detection of ctDNA may be associated with an increased risk of relapse. In some tumors, molecular signs are detected prior to the clinical or radiological manifestation of relapse.
This capability provides significant prognostic information and creates the prospect of more accurate risk stratification of patients. However, prognostic value does not inherently confirm clinical utility: identifying a patient group with a high risk of relapse does not automatically mean that altering treatment based on the test will improve survival or quality of life.
Therefore, the use of ctDNA in MRD assessment must be distinguished from the intensification, de-escalation, or modification of treatment based on its results. Such decisions require utility confirmed by appropriate clinical trials.
What Do Clinical Trials Show?
The DYNAMIC Trial: Colorectal Cancer
A significant example of a ctDNA-guided management strategy is the randomized DYNAMIC trial, conducted in patients with stage II colon cancer.
The trial compared a ctDNA-guided strategy for prescribing adjuvant chemotherapy with standard clinicopathological criteria-driven management. In the ctDNA-guided group, 15% of patients received adjuvant chemotherapy, compared to 28% in the standard management group. The two-year recurrence-free survival rates were 93.5% and 92.4%, respectively. The results demonstrated that in the studied population, the ctDNA-guided strategy reduced the use of chemotherapy without compromising recurrence-free survival compared to standard management.
Breast Cancer: Prognostic Value and Clinical Utility
The use of ctDNA in breast cancer is an area of active research. Existing evidence indicates that detecting molecular residual disease may have prognostic significance and help assess the risk of relapse.
However, it remains to be studied whether changing treatment based on ctDNA results improves patient survival and quality of life. Accordingly, the capabilities of routine MRD monitoring in early-stage breast cancer and guiding treatment with these results must be evaluated according to specific clinical evidence and current recommendations.
Can Liquid Biopsy Detect Relapse Before Radiological Manifestation?
Detecting molecular relapse prior to radiological relapse is one of the most intriguing directions of ctDNA research.
In some cases, tumor-derived DNA can be detected in the blood before the relapse site reaches a size detectable by standard imaging methods. Information obtained this way may facilitate an earlier assessment of relapse risk.
However, early detection does not mean that early intervention is necessarily effective. A positive ctDNA result may indicate molecular relapse without determining the anatomical location of the disease or indicating which treatment will be effective.
Furthermore, receiving information about a molecular relapse earlier may increase patient anxiety, the need for additional investigations, and the treatment-related burden if there is no evidence-based intervention that improves the final clinical outcome.
Therefore, clinical decision-making must evaluate not only the assay’s ability to detect a molecular alteration but also the practical benefit of actions taken based on this information.
2026 ASCO Guidelines: What Is Changing in Clinical Practice?
In 2026, the American Society of Clinical Oncology (ASCO) published a clinical practice guideline dedicated to ctDNA testing in solid tumors and lymphomas. The document summarizes existing evidence and defines clinical situations where the use of the test may be appropriate.
According to the guideline, ctDNA testing to detect genetic alterations of the tumor may be considered when:
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Tissue-based testing is difficult, impossible, or the biopsy poses an unacceptable risk to the patient;
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Tissue testing results cannot be obtained within a clinically required timeframe;
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The approved indication of an appropriate therapeutic drug permits or requires ctDNA testing.
If the ctDNA result is negative, non-informative, or inconsistent with the clinical picture, considering a tissue biopsy is necessary. Moreover, ctDNA testing should not be viewed as a universal substitute for other essential diagnostic methods.
The guideline also emphasizes that quantitative ctDNA metrics or overall cfDNA concentration should not be used as surrogate markers for tumor burden outside of clinical trials. Recommendations regarding MRD and molecular relapse assessment continue to evolve and require further accumulation of evidence based on tumor type and specific clinical applications.
Limitations and Challenges in Clinical Implementation
False-Negative Results
In the early stages of the disease or with a low tumor burden, the amount of ctDNA may fall below the assay’s limit of detection. Consequently, a negative result does not rule out the presence of residual disease or clinically actionable genetic alterations. In such cases, the interpretation of the result must be based on the test’s sensitivity and the clinical context.
Tumor Heterogeneity and Non-Tumor-Derived Alterations
Although plasma analysis may reflect information from several tumor sites, not all clones release detectable DNA into the blood. In addition, some genetic alterations may originate from non-tumor cells. A notable example is age-related clonal hematopoiesis, which in certain cases can complicate ctDNA interpretation. Therefore, considering the technical capabilities of the assay and potential alternative sources of the result is essential.
Cost and Equitable Access
Advanced molecular testing requires appropriate laboratory infrastructure, validated methods, trained personnel, and clinical interpretation. The cost of testing, reimbursement mechanisms, and subsequent access to targeted therapies may vary significantly across healthcare systems and patient populations.
In resource-constrained settings, it is particularly crucial to evaluate not only the technical accuracy of the test but also its cost-effectiveness, clinical utility, and equitable accessibility. Implementing innovative technology must not exacerbate inequalities among patients who have disparate access to diagnostics and modern treatment.
Future Perspectives
The further development of liquid biopsy will continue in several directions: improving analytical sensitivity, standardizing testing methods, integrating data from various biomarkers, and defining the clinical decisions where ctDNA provides the most benefit.
Prospective and randomized trials evaluating whether treatment intensification or de-escalation based on ctDNA improves overall survival, recurrence-free survival, and quality of life will be of paramount importance. Additionally, assessing treatment-related toxicity, the need for further investigations, and the financial burden is required.
Future research must answer not only how early we can detect molecular alterations but also how we should use this information to achieve tangible benefits for the patient.
Liquid biopsy, particularly ctDNA analysis, is one of the major evolving directions in precision oncology. Its application creates opportunities to detect actionable genomic alterations for treatment, assess the molecular evolution of the tumor, and determine the risk of relapse in cases where standard clinical or radiological assessment fails to provide complete information.
However, the technology’s potential must be evaluated with an evidence-based approach. The detection of a molecular alteration, its prognostic value, and the clinical utility of decisions made based on this information are distinct concepts.
The future of liquid biopsy will depend not only on how early and accurately we can detect tumor-derived DNA but also on whether we can utilize this information to improve treatment outcomes, quality of life, and patient-centered oncological care.
Author: Mariam Chirakadze, Medical Doctor (MD)
