A liquid biopsy may more accurately detect mutations in EGFR and KRAS genes in non-small cell lung cancer (NSCLC), a recent study suggests.

The test, also known as a rapid plasma genotyping, takes a test tube of blood containing free-floating DNA from cancer cells and analyzes it for mutations or abnormalities. This technique is commonly used in research for probing the molecular make-up of different types of cancers.

“We see plasma genotyping as having enormous potential as a clinical test, or assay -- a rapid, noninvasive way of screening a cancer for common genetic fingerprints, while avoiding the challenges of traditional invasive biopsies,” said senior study author Geoffrey Oxnard, MD. “Our study was the first to demonstrate prospectively that a liquid biopsy technique can be a practical tool for making treatment decisions in cancer patients. The trial was such a success that we are transitioning the assay into a clinical test for lung cancer patients at DF/BWCC.”

The study, published in JAMA Oncology, used 180 NSCLC patients, of which 120 were newly diagnosed and 60 had become resistant to prior treatment, causing recurrence.

The cell-free DNA was tested for mutations in the 2 genes, as well as for a separate mutation in EGFR that allows tumor cells to become resistant to front-line targeted drugs.

Researchers used the droplet digital polymerase chain reaction (ddPCR) to perform the tests. This technique involves counting the individual letters of the genetic code in the cell-free DNA to determine if the mutations are present.

Additionally, patients had to have a conventional tissue biopsy to test for the same mutations. The liquid biopsy results were then compared with tissue biopsies.

The results of the study showed that the liquid biopsy produced results faster than the tissue biopsy. The median turnaround time in liquid biopsies was just 3 days, compared with 12 days for tissue biopsies in newly diagnosed patients and 27 days for patients who are drug resistant.

The predictive value of plasma ddPCR was 100% for the primary EGFR and KRAS mutation, meaning patients had these mutations in their tumor.

The predictive value for patients with the EGFR resistance mutation was 79%, suggesting that the blood test was able to find further cases with the mutation originally missed by standard biopsies.

“In some patients with the EGFR resistance mutation, ddPCR detected mutations missed by standard tissue biopsy,” Oxnard said. “A resistant tumor is inherently made up of multiple subsets of cells, some of which carry different patterns of genetic mutations. A single biopsy is only analyzing a single part of the tumor, and may miss a mutation present elsewhere in the body. A liquid biopsy, in contrast, may better reflect the distribution of mutations in the tumor as a whole.”

When ddPCR was unable to detect the mutations, the results were unclear, indicating that the tumor cells don’t carry the mutations or that the tumor isn’t shedding its DNA into the bloodstream. The discrepancy was found to be less common in patients with metastatic cancer.

The liquid biopsy shows promise in helping physicians quickly determine if a patient is responding to therapy. In the study, 50 participants had repeat testing after starting cancer treatment.

“Those whose blood tests showed a disappearance of the mutations within 2 weeks were more likely to stay on the treatment than patients who didn't see such a reduction,” said lead study author Adrian Sacher, MD.

The liquid biopsies can detect new mutations early, like those that are EGFR resistant and have the potential to be treated with targeted agents.

The liquid biopsy within the study proved so reliable that the Dana-Farber/Brigham and Women’s Cancer Center (DF/BWCC) became the first medical facility in the country to offer it to all patients suffering from NSCLC.

“The study data are compelling,” said DF/BWCC pathologist Lynette Sholl, MD. “We validated the authors' findings by cross-comparing results from liquid and tissue biopsies in 34 NSCLC patients. To work as a real-world clinical test, liquid biopsy needs to provide reliable, accurate data and be logistically practical. That's what we've seen with the ddPCR-based blood test.

“The test has great utility both for patients newly diagnosed with NSCLC and for those with a recurrence of the disease. It’s fast, it's quantitative (it indicates the amount of mutant DNA in a sample), and it can be readily employed at a cancer treatment center.”