By Deborah Borfitz 

April 6, 2023 | Circulating tumor DNA (ctDNA) holds potential as a biomarker in lung cancer clinical trials as an added and easier-to-monitor endpoint to survival rates for measuring treatment efficacy, according to Atocha Romero, PharmD, Ph.D., director of the liquid biopsy laboratory at the Puerta de Hierro Hospital in Madrid, Spain. This was one of the key findings of her most recent work (Journal of Clinical Oncology, DOI: 10.1200/JCO.21.02660), where ctDNA was also shown to outperform clinical responses assessed on CT scans in the prediction of survival. 

“Tumor biopsies can be challenging and at times limited for lung cancer patients, mostly due to the anatomical location of the tumor and the advanced age of these patients,” says Romero. “Our goal is to safely and efficaciously improve their options for testing and treatment.”  

Importantly, she says, the study employed digital polymerase chain reaction (PCR)—specifically, the Absolute Q system of Thermo Fisher Scientific, with whom her lab has been actively developing liquid biopsy technologies. Assays run on the system can detect rare alleles from a simple blood draw in many different types of cancer, based on the prognostic indicators first identified by next-generation sequencing analysis.   

The study was evaluating the long-term clinical benefit of chemoimmunotherapy treatment delivered to patients before surgery for stage IIIA non-small-cell lung cancer (NSCLC) and assessing the utility of ctDNA as a predictive factor and potential trial endpoint, Romero explains. The use of Response Evaluation Criteria in Solid Tumors (RECIST) to assess changes in solid tumor size in patients “may have some limitations,” she says, noting that it is “sometimes difficult to differentiate pseudoprogression from true progression in cancer patients treated with immunotherapy.” 

This highlights the importance of the “significant association” found between ctDNA levels after neoadjuvant chemoimmunotherapy and survival outcomes in operable NSCLC, continues Romero. While the trial was small (46 patients) and further study is needed, it suggests that ctDNA may be useful as a trial endpoint in the context of neoadjuvant treatment for certain types of lung cancer. 

However, she quickly adds, “ctDNA quantification needs to be standardized.” The pre-analytical phase, likewise, is not standardized and perhaps why some tumor-derived DNA fragments have gone undetected. 

“Numerous reports have shown that the baseline ctDNA level is a prognostic factor in a wide range of patients with lung cancer,” says Romero. It has been proposed to incorporate ctDNA levels into the widely used TNM staging system (based on tumor size and its nearby spread and metastasis), “which could potentially help with diagnosis and clinical staging.” 

This observation also held true in the latest trial, she says. “Of note, neither tumor mutation burden nor programmed cell death ligand-1 staining was predictive of survival.” 

Current Challenge 

“Liquid biopsies are increasingly used in daily oncology practice for non-invasive biomarker testing,” says Romero, but further research is needed to expand its role in the clinic. “We want to know if [such a test] can be useful to monitor disease, and if it can be used to guide clinical decision-making.” 

In the context of the latest study where a liquid biopsy was evaluating the effectiveness of neoadjuvant treatments, it could potentially provide a means to quickly as well as accurately measure the odds of long-term survival. “This could speed up the process of a clinical trial and therefore getting new therapies to patients.” 

In patients with NSCLC, a growing body of evidence supports the use of liquid biopsies for epidermal growth factor receptor (EGFR) testing, Romero says. “Nevertheless, robust methodologies for the identification of other alterations are still lacking.” 

The current challenge is to increase the sensitivity of blood tests for detecting complex variants, such as rearrangements in anaplastic lymphoma kinase (ALK), c-ros oncogene 1 (ROS1), RET receptor tyrosine kinase (RET), or neurotrophic tyrosine receptor kinase (NTRK) genes. “Detecting these fusions using liquid biopsies... could potentially expand therapeutic options in NSCLC patients.” 

In a study published earlier last year in Clinical Chemistry (DOI: 10.1093/clinchem/hvac021), Romero and her team used liquid biopsy in a preclinical model of NSCLC to look for ALK fusions in extracellular vesicles. “To our knowledge, this is the first study thoroughly demonstrating that ALK fusions are present and can be detected in extracellular vesicle preparations from ALK-positive NSCLC cells and plasma samples from NSCLC patients.”