Cancer's genetic fingerprint allows doctors to personalise treatment

Personalised blood tests will mean doctors can monitor how well a particular patient's cancer is responding to surgery or therapy

A personalised blood test that monitors cancer in the body and spots when it has returned after treatment has been developed by scientists.

Researchers believe the test will give doctors a way to tailor cancer treatments to individual patients by monitoring how well their tumour has responded to surgery or therapy and picking up the early signs of a recurrence.

In principle, the test could be used to keep watch over any kind of cancer that scientists can collect cells from.

Scientists developed the test after deciphering the full genomes of tumour tissue taken from six patients. Most cancers contain large-scale rearrangements of genetic material that aren't seen in healthy tissue, so they can be used as a genetic "fingerprint" for the tumour.

A patient who has recently been diagnosed with cancer will have high levels of a tumour's genetic fingerprint in their blood, because cancers shed cells and DNA into the bloodstream.

When a cancer is operated on or treated with radio- or chemotherapy, the levels of the fingerprint should fall, and vanish altogether if the tumour has been eradicated.

A team led by Victor Velculescu, professor of oncology at Johns Hopkins University in Baltimore, developed individual tests for six patients, four of whom had bowel cancer and two breast cancer.

Genetic tests on one patient with bowel cancer, for example, revealed that a chunk of one chromsome in the tumour had fused with another chromosome. This huge genetic glitch or "biomarker" was a major part of the tumour's genetic fingerprint.

Doctors found that after surgery, levels of the biomarker dropped in the patient, but then rose again, suggesting the cancer remained in their body. After chemotherapy and further surgery, the biomarker levels dropped substantially but not to zero. The residual level of cancer was traced back to a tumour that had spread to the patient's liver.

Scientists liken the technique to "searching for the genetic breadcrumb trail left by lingering cancer cells after surgery or during drug therapy". The work was announced today at the annual meeting of the American Association for the Advancement of Science in San Diego and appears in the journal Science Translational Medicine.

The test, known as personalised analysis of rearranged ends (Pare), could potentially be developed for any kind of cancer, according to Velculescu. "There is currently no test for cancer patients that provides personalised biomarkers for clinical management of disease, and we feel this is an important step," he said.

Reading the full genome of a patient's cancer currently costs around £3,200, but the price of the technology is falling rapidly as it improves. The researchers believe the Pare test will eventually be more cost-effective than standard hospital CT (computerised tomography) scans, which are less able to detect microscopic cancers.

The test relies on identifying rearrangements of large chunks of DNA rather than single-letter changes in the genetic code, which are more difficult to spot. "These alterations, like the re-ordering of chapters of a book, are easier to identify and detect in the blood than single-letter changes," said Bert Vogelstein, a co-author on the study.

The scientists began each test by first checking the tumour's genome for areas where it had too few or too many copies of DNA, and where large regions of chromosomes had fused.

These regions were analysed further to identify DNA sequences with incorrect ordering, orientation or spacing. Between four and 15 rearrangements were found in each of the six patients.

By amplifying tiny amounts of DNA in the patients' bloodstream that had the same rearrangements, the test was able to monitor changes in the size of the tumour.

"Eventually we believe this type of approach could be used to detect recurrent cancers before they are found by conventional imaging methods, like CT scans," said Luis Diaz, an oncologist at Johns Hopkins who took part in the study.

Professor Peter Johnson, chief clinician at Cancer Research UK, said: "This is another exciting step down the road towards personalised cancer medicine. The detection of DNA changes unique to individual cancers has proved to be a powerful tool in guiding the treatment of leukaemia. If this can be done for other types of cancer like bowel, breast and prostate it will help us to bring new treatments to patients better and faster than ever."

Dr Caroline Wright, head of science at UK health charity the Foundation for Genomics and Population Health, agreed. "This novel application of next generation sequencing technology potentially has enormous clinical benefits for monitoring treatment response and screening patients in remission," she said.

"However, evidence is still needed to show that this approach would actually allow recurrent cancers to be detected before they could be found by other conventional methods, such as imaging, and then treated before causing symptoms."


Ian Sample, San Diego

The GuardianTramp

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