In advanced non–small cell lung cancer (NSCLC), combining plasma-based next-generation sequencing (NGS) with tissue testing meaningfully increases the identification of targetable alterations, which translates into more patients receiving precision therapies.

Multiple studies, including one with data from our own group at the University of Pennsylvania, have shown that liquid biopsy, or plasma-based circulating tumor DNA (ctDNA) NGS, can meaningfully increase the detection of actionable biomarkers in advanced NSCLC. In stage IV disease, a complementary approach that combines tissue- and plasma-based testing yields a higher detection rate than either approach alone.

Our cohort study in patients with metastatic NSCLC showed that incorporating plasma NGS alongside tissue testing not only increased the identification of targetable mutations but also translated into a greater use of precision therapies. Liquid biopsy offers the practical advantage of being minimally invasive and having the ability to identify driver mutations even when tissue is insufficient or unobtainable. In our cohort, plasma NGS alone detected mutations in a substantial proportion of patients who could not complete tissue testing.

That said, it is important to be mindful of the limitations of liquid biopsy. False-negative results remain a recognized limitation of the plasma-based approach. One of the reasons for this is that ctDNA shedding may be inadequate for detection in some patients, despite the presence of an actionable driver. Clinicians should therefore interpret negative liquid biopsy results with caution in this context.

It is also strongly recommended to perform both DNA- and RNA-based NGS whenever possible. RNA-based testing is particularly important for detecting gene fusions and certain splicing alterations, including MET exon 14 skipping mutations. Not all commercial assays automatically include RNA sequencing, so the deliberate selection of testing platforms that incorporate RNA analysis or reflex RNA testing is critical to avoid missing these actionable alterations.

While plasma ctDNA has matured into a standard guideline-endorsed tool, with prospective data showing that it meaningfully augments tissue testing and guides therapy in advanced NSCLC, the situation with cerebrospinal fluid liquid biopsy is a bit more unsettled. There are some research efforts aimed at detecting central nervous system metastases in NSCLC using ctDNA compared with cerebrospinal fluid cytology; however, clinical validation is needed, and we simply do not have the evidence to integrate it into the clinic routinely at this time.

Also on the research horizon, strategies incorporating ctDNA continue to evolve rapidly, and ongoing studies using liquid biopsy approaches are of particular interest. For example, Helena A. Yu, MD, is leading a ctDNA-adaptive phase 2 trial using early plasma EGFR ctDNA clearance after osimertinib initiation to guide treatment adaptation (ie, the continuation of osimertinib monotherapy vs escalation to osimertinib plus chemotherapy).