Minimally and noninvasive molecular diagnostics hold the potential to change the prognostic measures physicians use daily in clinical medicine dramatically. Leading the way are liquid biopsies—tests that are able to harvest and sequence tumor DNA from patients’ blood samples.
Now this simple blood test can rapidly and accurately detect mutations in two key genes from non-small-cell lung cancer (NSCLC). A collaborative research group led by scientists at the Dana-Farber Cancer Institute has demonstrated the test's potential as a clinical tool for identifying patients who can benefit from drugs targeting those mutations.
The results from this new liquid biopsy study proved so reliable that the Dana-Farber/Brigham and Women's Cancer Center (DF/BWCC) this week became the first medical facility in the country to offer it to all NSCLC patients, either at the time of first diagnosis or of relapse following previous treatment.
NSCLC is the most common form of lung cancer, diagnosed in more than 200,000 people in the U.S. each year, according to the American Cancer Society. An estimated 30% of NSCLC patients have mutations in either of the genes included in the study and can often be treated with targeted therapies.
The liquid biopsy tested in the study—technically referred to as rapid plasma genotyping—involves taking a test tube of blood and analyzing the tumor DNA for mutations or other abnormalities. This technique provides clinical investigators with a “snapshot” of key genetic irregularities in a tumor and is a common tool in research for probing the molecular makeup of different kinds 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,” explained senior study author Geoffrey Oxnard, M.D., thoracic oncologist and lung cancer researcher at Dana-Farber and Brigham and Women's Hospital. “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 findings from this study were published recently in JAMA in an article entitled “Prospective Validation of Rapid Plasma Genotyping for the Detection of EGFR and KRAS Mutations in Advanced Lung Cancer.”
The study recruited 180 patients with NSCLC, 120 of whom were newly diagnosed and 60 of whom had become resistant to a previous treatment, allowing the disease to recur. Patients’ cell-free DNA was tested for mutations in the EGFR and KRAS genes, and for a separate mutation in EGFR that allows tumor cells to become resistant to frontline targeted drugs. Using droplet digital PCR (ddPCR), the researchers were able to count the individual letters of the genetic code in cell-free DNA to determine if specific mutations are present. Each participant also underwent a conventional tissue biopsy to test for the same mutations. The results of the liquid biopsies were then compared to those of the tissue biopsies.
Remarkably, the data showed that liquid biopsies returned results much more rapidly, as the median turnaround time for liquid biopsies was 3 days, compared to 12 days for tissue biopsies in newly diagnosed patients and 27 days in drug-resistant patients.
Moreover, the liquid biopsy was found to be extremely accurate. The predictive value of plasma ddPCR was 100% for the primary EGFR mutation and the KRAS mutation—meaning that a patient who tested positive for either mutation was certain to have that mutation in his or her tumor. For patients with the EGFR resistance mutation, the predictive value was 79%, suggesting the blood test was able to find additional cases with the mutation that were missed using standard biopsies.
“In some patients with the EGFR resistance mutation, ddPCR detected mutations missed by standard tissue biopsy,” Dr. Oxnard noted. “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.”
And because tumors are constantly evolving and acquiring additional mutations, repeated liquid biopsies can provide early detection of a new mutation—such as the EGFR resistance mutation—that can potentially be treated with targeted agents.
“The study data are compelling,” said DF/BWCC pathologist Lynette Sholl, M.D. “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.”
Dr. Sholl added that “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, and it can be readily employed at a cancer treatment center.”