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Blood Test Locates Gene Defects Linked to Cancer

By Labmedica International staff writers
Posted on 21 Jan 2014
Image: The Nanodrop 1000 Spectrophotometer (Photo courtesy of Thermo Fisher Scientific).
Image: The Nanodrop 1000 Spectrophotometer (Photo courtesy of Thermo Fisher Scientific).
A simple blood test could be developed to determine whether gene mutations associated with pancreatic cancer exist without the need of locating and testing tumor tissue.

This blood test appears possible following the discovery that tiny particles called exosomes, which are shed by cancer cells into the blood, contain the entire genetic blueprint of cancer cells and by decoding this genomic data and looking for deletions and mutations associated with cancer; these findings could be translated into a test that helps physicians detect cancer.

Scientists at The University of Texas MD Anderson Cancer Center (Houston, TX, USA) collected serum samples on the day of surgery from patients undergoing surgical resection of their tumors. The team investigated whether exosomes from pancreatic cancer cells and serum from patients with pancreatic ductal adenocarcinoma contain genomic DNA.

Exosomes were isolated from the serum samples and cell cultures. DNA was extracted and other techniques such as flow cytometry analysis, western blots were performed. The amount of DNA from cells and cell-derived exosomes was quantified using a Nanodrop 1000 Spectrophotometer (Thermo Fisher Scientific; Wilmington, DE, USA). Whole genome sequencing was performed using the ThruPLEX-FD library prep technology (Rubicon Genomics; Ann Arbor, MI, USA) in combination with the HiSeq2000 sequencing platform (Illumina; San Diego, CA, USA).

The scientists found evidence that exosomes contain greater than 10 kilobase (kb) fragments of double-stranded genomic DNA. Mutations in the V-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS) and the tumor protein p53 can be detected using genomic DNA from exosomes derived from pancreatic cancer cell lines and serum from patients with pancreatic cancer. In addition, using whole genome sequencing, they demonstrate that serum exosomes from patients with pancreatic cancer contain genomic DNA spanning all chromosomes. These results indicate that serum derived exosomes can be used to determine genomic DNA mutations for cancer prediction, treatment, and therapy resistance.

Raghu Kalluri, MD, PhD, the senior author of the study, said, “At the present time, there is no single blood test that can screen for all cancer related DNA defects. 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.” The study was published on January 7, 2014, in the Journal of Biological Chemistry.

Related Links:

The University of Texas MD Anderson Cancer Center
Thermo Fisher Scientific 
Rubicon Genomics



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