Detecting cancers -- from tiny bits of tumor DNA in blood

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When cancer blooms in the body, tiny bits of tumor DNA can be found in the blood. Cancer specialists would love it if these DNA fragments could one day be used in noninvasive diagnostic tests -- “liquid biopsies” -- that are relatively inexpensive and sensitive. There’s a lot of work going on in this area right now.

One team of researchers reported a step toward that goal in a paper published Wednesday in the journal Science Translational Medicine. They used a strategy that can detect many different mutations in some key genes known to be involved in cancer even though the pieces of DNA from them were present in the blood plasma at low levels. Such a test, they say, would not have to be tailor-made for each cancer patient because it can look at a lot of different mutations at once, and that would make it cheaper and more practical.

The researchers, of Cambridge, England, showed that their strategy could track the progression of disease in advanced ovarian and breast cancer patients fairly accurately. They could see when a patient responded to treatment (plasma levels of key DNA fragments fell) and when they stopped responding to treatment (plasma levels of the DNA fragments started to rise again).


In a case that illustrates how they think their technology could be used, the scientists described a patient who’d had tumors in the bowel and ovary. She had surgery, and responded well to it. Five years later, however, she developed a mass in the pelvis and the doctors weren’t sure which tumor it had come from. It was not biopsied because that was deemed too dangerous, so doctors proceeded with their best bet for a course of treatment –and the patient did, in fact, respond to it.

The authors of the paper did an after-the-fact genetic analysis of the patient’s plasma and tumors. They found that the bowel and ovarian tumors had different genetic mutations in them – and that the patient’s plasma at the time of relapse contained the mutations corresponding to the bowel tumor, not the ovarian tumor. “Had these results been available, uncertainty and treatment delays may have been avoided, as well as the risk of prescribing chemotherapy for an inappropriate tumor site,” wrote Tim Forshew, of the Cancer Research UK Cambridge Research Institute, and his colleagues.

There are a variety of ways that such technology could be helpful one day in cancer treatment, the scientists say:

Doctors could see what mutations were behind a patient’s cancer and when new mutations were added as time went by and the cancer mutated further. Cancer, as it’s often been said, isn’t a single disease: There are many different ways that cells of the body can go rogue and start growing out of control and spreading.

What’s more, analysis of plasma would offer a noninvasive “whole body” look at all the cancer growing in a person’s body. Since cancers mutate and change over time, one tumor in the same body could contain mutations not present in another one. With a plasma screen, bits of DNA from all of them would be floating around and be detected.

Because a test like this could help cancer doctors know just which genes are responsible for Person A’s cancer versus Person B’s cancer, it might help them decide which drugs and therapies to give a patient. (Some drugs are helpful for some types of cancer and not others.) As new mutations arose, they could change the therapy if appropriate.


Doctors could track how well therapy was working, and test to see if the cancer was returning in patients who had been responding to treatment.

And maybe such tests could one day be used to detect certain dangerous cancers that are currently hard to detect until they’re quite advanced, such as ovarian cancers.