Blood test that locates gene defects associated with cancer could be on the horizon

The presence of gene mutations associated with pancreatic cancer could potentially be determined with a simple blood test. This appears possible because of the discovery that tiny particles the size of viruses called exosomes, which are shed by cancer cells into the blood, contain the entire genetic blueprint of cancer cells.

By decoding this genomic data and looking for deletions and mutations associated with cancer, the research team believes this discovery could be translated into a test that helps detect cancer and treat patients. The findings are based on research led by Raghu Kalluri, MD, PhD, chairman and professor in the Department of Cancer Biology at The University of Texas MD Anderson Cancer Center in Houston. The research results appear in the Journal of Biological Chemistry (2014; doi:10.1074/jbc.C113.532267).

“At the present time, there is no single blood test that can screen for all cancer-related DNA defects,” said Kalluri. “In many cases, current protocols require a tumor sample to determine whether gene mutations and deletions exist and therefore determine whether the tumor itself is cancerous or benign. To procure tumor tissue, one needs to know that a tumor exists and if so, is it accessible for sample collection or removal? Finally, there are always risks and significant costs associated with surgical procedures to acquire tumor tissue.”

Historically, researchers were aware that these miniscule particles existed and that they carried nucleic acids and proteins. Exosomes were also believed to carry small portions of the person's DNA. However, upon further investigation, the research team was surprised to learn that the person's entire double-stranded genomic DNA—which spans all chromosomes—can be found in exosomes, including those mutated chromosomes that cause various cancers. Furthermore, they discovered that DNA derived from exosomes carried the same cancer-related genetic mutations when compared with the cancer cells taken from tumor.

“Because different forms of cancer are associated with different chromosomal mutations, we believe analysis of exosome DNA taken from blood samples may not only help determine the presence of a cancerous tumor somewhere in the body, but also identify mutations without a need for tumor sample,” added Kalluri. “We also believe this fingerprint will help lead us to the likely site of the tumor in the body. For instance, certain mutation spectrums would suggest pancreatic cancer or a brain-based tumor. Although there is much more work to be conducted to develop such a test, having a tool such as this would increase our abilities to detect cancer in an earlier stage and therefore increase our chances of effective treatment.”

“This seminal discovery paves the way for highly sensitive screening for driver mutations of cancer in the blood without the need for biopsy of tumor tissue and, importantly, lays the foundation for a new method for the early detection of cancer when the chance for cure is greatest,” said MD Anderson President Ronald A. DePinho, MD.

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