GENEVA – Blood sampling provides a less invasive alternative to tumor biopsy for collecting cancer DNA for mutation testing, but retrieving tumor DNA from a patient’s urine is least invasive of all.
In an early phase of clinical investigation, researchers assessed the feasibility of using urine to collect cell-free tumor DNA to detect mutations in 34 patients with advanced non–small cell lung cancer. The results suggested that testing circulating tumor (ct) DNA isolated from patients’ urine was sensitive compared with testing DNA from biopsied specimens of the primary tumor, and it was able to flag tumor changes early, before clinically-identifiable effects appeared, Dr. Hatim Husain said at the European Lung Cancer Conference.
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Dr. Hatim Husain
He used ctDNA isolated from patients’ urine to test for the presence of three different resistance mutations within the epidermal growth factor receptor (EGFR) gene. Genetic testing of biopsy specimens showed 10 patients carried the T790M mutation, 18 carried an exon 19 deletion, and eight carried an exon 21 L858R mutation. Of these 36 mutations in 34 patients, testing ctDNA isolated from urine identified 35 as positive, a 97% overall concordance rate.
In addition, testing with ctDNA from urine also picked up three additional T790M mutations not seen in the three corresponding tumor-biopsy specimens, but in patients with high clinical suspicion for carrying an EGFR mutation, Dr. Husain reported.
Further evidence for the utility of urinary ctDNA came from following 22 patients on treatment with erlotinib (Tarceva) and monitored for their acquisition of an EGFR-gene mutation making the tumor erlotinib resistant. Dr. Husain and his associates ran a DNA test every 3-6 weeks and tracked the time until patients developed radiographic progression. Using urinary ctDNA, they found four patients who developed EGFR mutations 29-111 days before clinical progression of the tumor became radiographically apparent.
The ctDNA that ends up in a patient’s urine starts out circulating in the blood; urine works as the main elimination route. Urine ctDNA is more concentrated than in blood, and ctDNA remains stable in urine at ambient temperature for 2 weeks, said Dr. Husain, an oncology researcher at the University of California San Diego, La Jolla.
“These interim results suggest that use of urinary ctDNA has potential to detect EGFR T790M status in a higher number of study subjects and may make some patients eligible for therapy who would by tissue biopsy be falsely classified as negative,” Dr. Husain said in a written statement. “Detecting the emergence of EGFR T790M mutations before progression has the potential to enable physicians to better align therapeutic selection and inform early therapeutic decision making,” he said.
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Dr. Egbert F. Smit
Testing ctDNA in patients’ urine is a “novel way to do noninvasive testing,” said Dr. Egbert F. Smit, professor of pulmonary medicine at VU University Medical Center in Amsterdam and the meeting’s designated discussant for Dr. Husain’s report. “It’s attractive for collecting ctDNA because you get a high concentration, and it has potential for a high level of sensitivity. It may have potential for showing how a tumor reacts to treatment. The method seems robust, but we still need data on reproducibility and cost effectiveness,” Dr. Smit cautioned.
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