When a person receives a diagnosis of cancer, or there is suspicion, the same concern usually appears: When can a liquid biopsy provide useful information in cancer? The answer depends on the clinical moment and what needs to be known: confirm or profile the tumor, guide treatment, monitor response, or detect recurrence. In practice, this test can be a valuable alternative when a tissue biopsy cannot be performed or when looking for repeatable molecular information with a minimally invasive procedure.
Liquid biopsy is based on the analysis of components of the tumour that circulate in body fluids, especially in blood. Its strength is not in always “replacing” traditional biopsy, but in complementing diagnosis and follow-up with genetic and epigenetic data that change over time.
What is liquid biopsy and how does it work in cancer?
Liquid biopsy identifies tumor biomarkers in blood (and in some cancers, in other fluids). Among the most studied are circulating tumor cells and circulating tumor DNA (ctDNA within cfDNA). By analyzing these markers, tumor burden can be estimated, somatic mutations detected, treatment-associated changes observed, and, in certain contexts, relapses can be anticipated.
Circulating Tumor Cells: Detection and Analysis
Circulating tumor cells are cancer cells that break off from the tumor (or metastasize) and pass into the bloodstream. Its presence is associated with risk of dissemination and with the evolution of the disease. The literature describes how the detection of circulating tumor cells helps to identify patients with a higher probability of metastasis and to monitor the course of the cancer.
These cells retain traits of the tumor of origin, which allows them to study relevant characteristics and support therapeutic decisions when tissue is scarce or difficult to obtain.
circulating tumor DNA as biomarkers (cfDNA and ctDNA)
cfDNA (free DNA) circulates in plasma, within which a fraction of ctDNA that comes from the tumor can be found. This ctDNA may contain mutations that guide molecular diagnosis, estimate tumor burden, and mark pathways of resistance to treatments.
DNA methylation is also studied, which provides epigenetic information complementary to mutations. In certain scenarios, the methylation pattern helps to increase detection capacity and to refine therapeutic follow-up, always interpreted together with the clinical picture and other tests.
When does liquid biopsy provide useful information in diagnosis?
Diagnostic utility is usually greatest when low-risk molecular information is needed or when the tumor cannot be safely sampled. In Panama, this is relevant in patients with comorbidities, complex access to the tumor or the need for repeatable results over time without invasive procedures.
When tissue biopsy is not possible or safe
There are tumors that are difficult to access due to their location or the general condition of the person, where a tissue biopsy involves more risk than acceptable. In those cases, a liquid biopsy can provide important data on circulating tumor DNA or cancer cells in the blood, reducing the risk of the procedure.
Even with that benefit, a negative result does not rule out cancer; Performance depends on tumor type and stage.
Mutation detection for precision medicine
One of the most common reasons for ordering liquid biopsy is to look for mutations that define sensitivity or resistance to targeted therapies. The mutation profile detected in ctDNA can guide the choice of treatment and serve as a baseline for comparing subsequent changes.
This approach is especially useful when the tumor is heterogeneous or when a single piece of tissue does not reflect the entire tumor biology.
Identification of biomarkers in breast cancer and pancreatic cancer
In breast cancer, liquid biopsy can detect mutations associated with therapeutic resistance and biomarkers that support decisions during systemic management.
In pancreatic cancer, where early diagnosis is difficult, the detection of alterations in ctDNA or methylation patterns is explored as a support for early detection in selected clinical contexts, always with caution due to sensitivity limitations in early stages.
Usefulness of liquid biopsy in treatment follow-up
A practical advantage of liquid biopsy is that it can be repeated. This allows us to observe the disease as a process that changes, not as a still photo of a single day.
Monitoring the response to chemotherapy
During chemotherapy, ctDNA quantification may reflect changes in tumor burden. When levels decrease steadily, it usually suggests a good response; If they are maintained or increased, it may indicate that treatment is not controlling the disease as expected.
This monitoring is not a substitute for imaging or clinical evaluation, but it does provide a molecular layer that sometimes anticipates radiological changes.
Early detection of treatment resistance
ctDNA can show the appearance of new mutations that explain resistance. The scientific review highlights the value of detecting these signs before progression is evident in clinical or radiology.
This information can help to rethink the therapeutic approach more quickly, always within the comprehensive assessment of the case.
Assessment of tumour burden during treatment
The serial measurement of biomarkers, either ctDNA or circulating tumor cells, allows tumor burden to be estimated in an objective and repeatable way. In practice, it is interpreted together with traditional markers, symptoms, physical findings and images, avoiding decisions based on a single isolated piece of data.
Liquid biopsy to detect recurrence and residual disease
After treatment ends, many people live with the worry of a relapse. During this period, the liquid biopsy is studied and applied as a support to identify early signs of tumor return.
Detection of minimal residual disease
Minimal residual disease refers to the persistence of tumor cells or tumor material after treatment, even when conventional tests appear normal. Liquid biopsy can detect trace amounts of ctDNA with high sensitivity in selected settings, opening the door to closer monitoring or early interventions when the risk warrants.
Prediction of late recurrence in breast cancer
In breast cancer, the detection of ctDNA after treatment can anticipate a late recurrence months in advance of clinical or radiological manifestations. That signal is not a sentence in itself, but it allows for adjusting follow-up and discussing therapeutic strategies when appropriate.
Post-treatment surveillance in different types of cancer
Not all tumors release ctDNA in the same amount, nor do they do so at the same time. Each type of cancer requires a surveillance strategy according to its biology and individual risk. Liquid biopsy can detect recurrence even when the original anatomical location makes repeated evaluations difficult, always understanding that false negatives may occur.
Types of cancer where liquid biopsy is most effective
Clinical performance varies. In general, tumors with higher release of biomarkers into the bloodstream tend to be more detectable.
Applications in Metastatic Breast Cancer
In metastatic breast cancer, more ctDNA and more circulating tumour cells are usually found in the blood, which favours their analysis. Molecular information can guide adjustments of systemic therapies and assess resistance.
Usefulness in pancreatic cancer and early detection
In pancreatic cancer, the interest is in supporting earlier detection and improving the selection of therapeutic strategies when there is already a diagnosis. Identifying mutations in plasma can help define candidates for surgery, neoadjuvant treatments or therapeutic changes, always with careful interpretation due to the variable sensitivity in the initial phases.
Liquid biopsy in bladder cancer (includes urine biopsy)
Bladder cancer offers a particular approach: blood and urine biopsy may be studied to detect cancer cells or tumor DNA. Urine testing can complement blood findings and increase the chance of detecting signs when the tumor is related to the urinary tract.
Limitations and Considerations of Liquid Biopsy
Liquid biopsy adds value, but it is not infallible. Knowing your limits prevents misinterpretations and unrealistic expectations.
Sensitivity and specificity in early stages
In early stages, the tumor can release very low amounts of ctDNA or circulating tumor cells, reducing sensitivity. Specificity must also be taken care of to avoid false positives that generate distress or inappropriate clinical decisions. The balance depends on the context and the objective of the test.
False negatives and technical limitations
A negative result does not rule out cancer or confirm the absence of residual disease. It can occur due to low release of biomarkers, tumor characteristics, or limits of the analytical method. For this reason, molecular data is integrated with images, pathology, laboratory and clinical evolution.
Need for standardization of detection techniques
There are differences between platforms, sampling, storage, extraction and analysis processes. Standardization is key to having comparable results over time. In follow-up, the consistency of the method and the laboratory can be as important as the point result.
Future of liquid biopsy in cancer management
Research is moving toward more sensitive tests, broader panels, and analyses that integrate genetics with epigenetics.
Advances in sensing techniques and technologies
Next-generation sequencing and bioinformatic analysis have expanded the ability to detect mutations at low frequencies, identify methylation patterns, and improve the reading of tumor signals in blood. As these technologies mature, their impact is seen in diagnosis, therapeutic selection, and surveillance, with more consistent results across clinical scenarios.
Integration with genetic and molecular analysis
The next step is to integrate ctDNA/cfDNA findings with clinical data, imaging, and pathology, to build decisions that are more closely aligned with the actual molecular profile of the tumor at each stage. This integration also helps to interpret subtle changes: a new mutation, an upward trend in ctDNA, or a signal compatible with residual molecular disease.
FAQ (Frequently Asked Questions)
¿La biopsia líquida reemplaza la biopsia de tejido?
Not always. Tissue biopsy remains key in many diagnoses, especially to confirm the type of cancer and its histology. Liquid biopsy is usually complementary when molecular information is required, when tissue cannot be obtained, or when repeated follow-up is needed.
¿Qué diferencia hay entre cfDNA y ctDNA?
cfDNA is circulating free DNA that comes from different cells in the body. ctDNA is the fraction of that cfDNA that comes from the tumor and contains somatic mutations or other changes relevant to cancer.
¿Puede detectar cáncer en etapas tempranas?
It can help, but its sensitivity is low in the early stages because the tumor releases little material into the bloodstream. Therefore, a negative result does not rule out disease and should always be interpreted in conjunction with other studies.
¿Sirve para ver si la quimioterapia está funcionando?
Yes, in many cases it can support follow-up. If ctDNA decreases during chemotherapy, it usually suggests a response; if it increases or reappears, it may indicate resistance or progression. Even so, it is not interpreted in isolation.
¿Qué es la minimal residual disease o enfermedad molecular residual?
Tumor is the presence of molecular signals from the tumor after treatment, even if it is not seen on images. Liquid biopsy can detect residual ctDNA in selected scenarios and help anticipate risk of recurrence.
¿En qué cánceres suele ser más útil?
It usually provides more information when there is greater release of biomarkers, such as in advanced or metastatic disease. It is frequently used in breast cancer, and is also studied in pancreatic cancer and bladder cancer, where it may include urine biopsy.
Choosing a liquid biopsy makes sense when looking for actionable molecular information without subjecting the patient to an invasive procedure, or when follow-up requires repeated measurements over time. Its interpretation requires clinical context, because an isolated value rarely tells the whole story. In the hands of the treating team, it can be a practical tool for refining decisions in diagnosis, treatment and surveillance.
With clear clinical criteria, the key question remains: When can a liquid biopsy provide useful information in cancer?
