A new highly sensitive blood test – developed by researchers at Stanford University – uses single colour digital PCR to characterize genetic mutations in circulating cancer cells. The test is sensitive enough to detect as little as three mutated DNA molecules in a small sample volume of blood.
Unlike some other cancer blood tests, this new technique has the potential to be tailored toward any individual cancer type. The researchers published the details of this technology in The Journal of Molecular Diagnostics.
“For monitoring patient tumors, only a handful of blood tests are available which are limited to only several types of cancers,” said senior study author Dr. Hanlee P. Ji, Associate Professor in the Department of Medicine at Stanford University and Senior Associate Director of the Stanford Genome Technology Center. “Nearly all cancer patients require monitoring by whole body imaging, which can be costly, complex, and time-consuming.
“In contrast, molecular tests like the one we have developed will enable patients to be monitored at every visit, and thus have the potential for quickly tracking cancer growth and spread,” continued Ji. “Moreover, the test’s rapid turnaround and relatively low cost, especially compared to next-generation DNA sequencing, provide a potential opportunity for universal monitoring of more patients than is currently done.”
So far, the assay has only been used to identify the genetic basis of cancer in six patients. Five of these patients were diagnosed with colorectal cancer, while the sixth patient suffered from cholangiocarcinoma, a cancer affecting the bile ducts in the liver.
The PCR-based assay was customized for each patient’s cancer type, and successfully identified circulating tumor-derived DNA in 50 percent of the patients. The patients without detectable levels of cancer cells in the blood were undergoing treatment during the study, which may have affected the results.
In one patient, however, the assay detected three different mutations in the tumor DNA.
While methods involving fluorescent probes and next-generation sequencing can help doctors study tumor DNA, they often require the DNA to be amplified prior to analysis. This step has the potential to introduce errors into the sample, giving single-colour digital PCR an advantage as it does not require this step.
“This test is simple enough to set up and analyze without extensive training, and therefore, it can be implemented by anyone, making it highly accessible to any laboratory,” said primary author Christina Wood Bouwens, of the Stanford Genome Technology Center and the Division of Oncology, Department of Medicine, Stanford University School of Medicine, Stanford, California. “It has been truly motivating to work with a technology that will help transform the way that we monitor and treat individuals with cancer. I am excited to share our findings with the cancer research community.”