Blood test paired with gene sequencing to detect cancer

The ability to detect cancer DNA in the blood has been combined with genome sequencing technology in a test that could be used to screen for cancers, monitor cancer patients for recurrence, and find residual cancer left after surgery.

The test was developed from blood samples taken from seven patients with late-stage colorectal cancer, three patients with late-stage breast cancer, and from healthy people. The investigators looked for DNA that had been shed into the blood. Then, whole-genome sequencing technology was applied to the DNA that was found, allowing sequences from cancer patients to be compared with those from the healthy people. The scientists searched for tell-tale signs of cancer in the DNA, such as dramatic rearrangements of chromosomes or changes in chromosome number that occur only in cancer cells.

The researchers found no cancer-specific chromosome changes in the blood of the healthy persons, but they did find various cancer-specific alterations in the blood of all seven patients with colon cancer and three patients with breast cancer. Specialized bioinformatic approaches enabled alterations in a small fraction of the millions of DNA sequences in the blood sample to be detected.

“This approach uses the power of genome sequencing to detect circulating tumor DNA in the blood, providing a sensitive method that can be used to detect and monitor cancers,” says Victor Velculescu, MD, PhD, of Johns Hopkins Kimmel Cancer Center.

The investigators note that there may be less circulating DNA in early stage cancers, and, thus, these would be more challenging to detect without more extensive sequencing. As sequencing costs decrease, the investigators expect that detecting earlier-stage cancers may become more feasible.

Velculescu says that additional research will focus on determining how the new test could help doctors make decisions on treating patients. For example, the blood test could identify certain chromosomal changes that guide physicians to prescribe certain anticancer drugs or decide patient enrollment in clinical trials for drugs that target specific gene defects. Currently, physicians use cellular material biopsied from the original tumor to make these decisions, but tumor material can often be inaccessible or unavailable.

The new study builds on the research team's earlier work using genomic sequencing of DNA in the blood to find rearrangements of chromosomes. The previous work required samples of the original tumor and knowledge of DNA changes in that tumor to find those same changes in the blood. This new test has no need for original tumor samples and includes an analysis of changes in the copy number of chromosomes.

This new approach was published in Science Translational Medicine (2012; doi:10.1126/scitranslmed.3004742).
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