Liquid biopsy gains ground as a monitoring tool for immunotherapy trials
Liquid biopsy has moved from a conceptual alternative to tissue sampling into a clinically useful way to track cancer biology in real time. In this narrative review, investigators pulled together recent literature on the main liquid biopsy platforms and paired that overview with an update on US governmental clinical trials targeting immunotherapy and liquid biopsy. The focus was narrow in the right way: how tumor-derived material in blood and other bodily fluids can help detect cancer, predict treatment response, and monitor resistance as therapy unfolds.
The review centers on liquid biopsy as a source of tumor-derived signals rather than a single test. Circulating tumor cells, circulating tumor DNA, and tumor extracellular vesicles sit at the heart of the discussion. Each reflects a different biological layer of the disease. Circulating tumor DNA carries genetic fragments shed by cancer cells, offering a route to detect mutations and clonal shifts. Circulating tumor cells represent intact malignant cells traveling through the bloodstream. Extracellular vesicles extend the picture by packaging nucleic acids, proteins, and other molecular cargo that can mirror tumor behavior and immune escape.
Recent literature was broad, but the clinical question stayed focused
The literature search used a scoping-review framework across PubMed/Medline, Scopus, and Cochrane, with gray literature added to widen the net. The search window covered articles published from June 30, 2023, through October 30, 2024. After screening 2,645 articles from the three databases and 45 additional gray-literature articles, the review retrieved full text for 325 articles. The numbers point to a large and rapidly expanding evidence base, but also to a field that remains fragmented across tumor types, assay platforms, and clinical uses.
That fragmentation is not just an academic inconvenience. Liquid biopsy technologies are being pushed into several different roles at once: detection, prognosis, treatment selection, and surveillance for resistance. Those uses do not require identical levels of analytic sensitivity or clinical validation, so the same biomarker can be promising in one context and unreliable in another. A test that performs well for mutation tracking during targeted therapy may still struggle to define early response to immunotherapy, where tumor-immune dynamics can be uneven and delayed.
The biology explains the appeal. Traditional tissue biopsy captures a single moment from one site, while metastatic cancer often evolves across multiple compartments. Serial blood sampling can reveal tumor load, heterogeneity, gene mutations, and clonal evolution without repeating invasive procedures. In practical terms, that means oncologists may gain a chance to watch disease biology shift under therapeutic pressure rather than infer it from intermittent imaging or a one-time tissue specimen.
Immunotherapy trials are building the next layer of evidence
A separate update in the review identified 25 United States registered governmental clinical trials that combine immunotherapy and liquid biopsy. Twenty are recruiting, and five are not yet recruiting. The trial inventory is important because it shows the field moving beyond observational enthusiasm toward prospective testing in government-sponsored studies. These trials are designed around the central question of whether tumor markers circulating in blood can improve how immunotherapy is selected, timed, and monitored.
The clinical logic is strong. Immune checkpoint therapy and other immunotherapy approaches do not always produce immediate radiographic change, and apparent progression can reflect immune infiltration rather than true treatment failure. A blood-based marker may help distinguish biological response from misleading imaging patterns earlier in the course of treatment. It may also identify patients whose tumors are adapting through clonal escape, antigen loss, or other resistance mechanisms before a standard scan becomes informative.
One sentence captures the stakes: serial blood testing may become the earliest sign that immunotherapy is working, or failing.
Tumor markers in blood may change how resistance is detected
The review frames liquid biopsy as a tool for precision medicine, not simply a less invasive specimen collection method. Precision oncology depends on detecting actionable mutations, identifying therapeutic resistance, and understanding heterogeneity across lesions and over time. Liquid biopsy fits those needs because it can be repeated, and repetition matters when a tumor is under constant selective pressure from treatment.
Resistance often emerges through clonal evolution. A subclone that survives therapy can expand while other clones shrink, leaving a molecular footprint in circulating material. In theory, that footprint can warn clinicians that a regimen is losing control before symptoms worsen or imaging confirms progression. In practice, performance will depend on tumor burden, assay sensitivity, cancer subtype, and the specific circulating analyte being measured.
The review does not claim that liquid biopsy has replaced tissue. It has not. Tissue still provides histology, architecture, and spatial context that blood cannot. But liquid biopsy increasingly offers a complementary window into disease behavior, especially when repeated tissue sampling is difficult, risky, or impractical. For patients on immunotherapy, that distinction can affect whether treatment is continued, changed, or augmented with another strategy.
Validation remains the limiting step
Even with the surge in recent publications and the active US trial portfolio, the field still depends on careful validation. Different assays detect different markers, and not every circulating signal reflects viable cancer. False positives can arise from technical noise, biologic background, or nonmalignant shedding. False negatives remain possible when disease burden is low or when the tumor does not shed enough detectable material into the circulation.
The review’s literature yield suggests strong momentum, but momentum is not the same as clinical readiness. What matters next is whether prospective trials can link liquid biopsy findings to patient-centered outcomes, including response classification, treatment durability, and earlier recognition of resistance. If those links hold, liquid biopsy could shift from an adjunctive research tool to a routine component of oncologic decision-making in immunotherapy-heavy settings.
For now, the message is straightforward. Cancer biology is increasingly being measured in motion, not just at a single time point. Liquid biopsy is built for that problem, and the current US trial pipeline shows that immunotherapy research is testing the idea where it matters most: in prospective patient care rather than retrospective speculation.