Liquid biopsy for monitoring lung cancer treatment

The role of liquid biopsy in monitoring treatment response in lung cancer is evolving as blood-based molecular testing moves from specialist research into clinical pathways. By analysing circulating tumour DNA (ctDNA), clinicians may track molecular change, identify acquired drug resistance and assess whether therapy is affecting disease between imaging appointments. The approach complements tissue pathology and radiology; it does not replace them.

For Australian patients, the appeal is a repeatable blood test that can support personalised treatment while avoiding repeated biopsies when a safer procedure is appropriate. Its value depends on choosing the right assay, timing samples carefully and interpreting results within the full clinical picture. Research translation is therefore as important as the technology itself.

From blood samples to molecular signals

Most liquid biopsies used for solid tumours analyse plasma. Targeted PCR or digital PCR can track a known mutation, while next-generation sequencing surveys multiple cancer genes and can reveal resistance mechanisms. Other approaches measure circulating tumour cells, DNA methylation or fragments of cell-free DNA. Each method answers a different question, so “liquid biopsy” should not be treated as a single test.

ctDNA is released by tumour cells into the bloodstream, but the amount varies with tumour burden, location, treatment and disease biology. A rising level may suggest progression; a falling level may accompany response, although inflammation or normal DNA can complicate interpretation. Cross-institutional perspectives, including HARP research resources, help teams compare how laboratory signals are validated and translated into clinical decisions.

Evidence for treatment response monitoring

In metastatic non-small-cell lung cancer (NSCLC), serial ctDNA testing can be especially useful when an actionable mutation is already known. For example, tracking EGFR variants during osimertinib treatment may help identify resistance such as T790M, while broader panels can monitor MET amplification or new kinase-domain changes. A result can prompt reassessment of treatment or tissue biopsy before therapy is changed.

Evidence also suggests that early ctDNA reduction, or molecular clearance, can precede improvements seen on CT in some settings. This is promising for immunotherapy, where conventional biomarkers do not always predict benefit. However, thresholds and assays differ between studies, and a negative plasma result cannot exclude cancer or a resistant clone, particularly with brain-only or low-volume disease.

After surgery for earlier-stage disease, ctDNA may help identify minimal residual disease and recurrence risk. This use remains investigational in many Australian centres and requires evidence from prospective trials, with clear pathways for confirmatory testing and rapid treatment access. Until then, liquid biopsy should complement imaging, pathology and multidisciplinary review rather than direct treatment alone.

Fitting monitoring into Australian care

Queensland lung cancer teams in Brisbane and across major public hospitals can build monitoring into existing multidisciplinary clinics. Australia’s mixed public and private pathology market creates options for sequencing expertise, but access is uneven. Medicare rebates through the Medical Benefits Schedule cover many standard tests, while specialised ctDNA panels may rely on hospital funding, research grants, clinical trials or private payment; PBS support for medicines does not automatically fund the assay.

Geography matters as much as assay design. Samples sent from Townsville, Cairns and other regional centres may face overnight courier and laboratory turnaround times that make timely treatment decisions difficult. Local collection linked to central next-generation sequencing can preserve quality, but protocols should specify acceptable delays, sample rejection criteria and a plan for reviewing results in Brisbane, Melbourne or another treating centre.

Equity also extends beyond test availability. Aboriginal and Torres Strait Islander patients should be involved in decisions about specimen use, data access and follow-up, with culturally safe consent processes and strong links to Aboriginal Medical Services and local clinicians. Any home-monitoring model must address consent for continuous data and secondary research use; the debate on ethical wearable monitoring offers a useful parallel for liquid-biopsy data governance.

Comparing liquid biopsy with tissue and imaging

No single modality answers every clinical question. The appropriate choice depends on whether the immediate need is molecular profiling, tissue diagnosis, anatomical staging or evidence of change over time.

Combining approaches is often strongest. A positive, clinically plausible ctDNA result can reveal heterogeneity missed by one biopsy, while tissue sampling remains necessary when plasma is negative or histology is required. For patients receiving immunotherapy, treatment toxicities and steroid exposure must be documented because they form part of the clinical context. Broader discussions such as this steroid-sparing review can prompt that attention, but they are not direct evidence for ctDNA monitoring.

A practical pathway for Australian lung cancer teams

A dependable pathway needs a defined clinical question, a validated assay and rules for acting on the result. The same blood sample may support baseline molecular profiling and serial monitoring, but intended use, turnaround and interpretation should be agreed before testing begins.

• Set the intended use and choose an assay with appropriate sensitivity for the disease burden and target.
• Standardise collection timing, transport, turnaround, reporting and thresholds for clinical escalation.
• Confirm unexpected or negative findings with tissue testing when the result will change management.
• Audit access, cost, turnaround and outcomes across metropolitan, regional and Aboriginal and Torres Strait Islander communities.

Governance should cover informed consent, genomic data, confidentiality, conflicts of interest and the pathway for rapid clinical review. Research results also need quality controls, external validation and post-implementation review so that a useful signal becomes a safe clinical service. Australian research and clinical partnerships can test these workflows before wider implementation.

Clinicians and research teams can coordinate this work with Brisbane Diamantina Health Partners, connecting pathology, imaging, ethics and patient voice. Start by mapping one multidisciplinary lung cancer clinic, selecting a laboratory partner and defining the first patient cohort and outcome to evaluate, with patients, families, carers and community representatives involved from the outset.