Cancer DNA in the blood can signal breast cancer’s return long before scans spot it, a new study shows.
A blood test that identifies tumor DNA circulating in the blood predicted 80 percent of breast cancer relapses after surgery and chemotherapy, researchers report August 26 in Science Translational Medicine. The blood test detected cancer recurrence nearly eight months — and in some cases, more than a year — before tumors were visible in scans.
“Now we have to figure out what to do with this information,” says Massimo Cristofanilli, a medical oncologist at Northwestern University Feinberg School of Medicine in Chicago. He was not involved in the research, but says that sort of lead time may one day give doctors a jump on the cancer to prevent it from becoming established in the bone, brain or other parts of the body. Unfortunately, there aren’t yet any effective treatments for stopping breast cancer spread, he says.
In the study, researchers took blood samples from 55 women who had started chemotherapy before undergoing surgery to remove breast tumors. Those women were at moderate to high risk of having their cancer come back, says coauthor Nicholas Turner, a medical oncologist at the Royal Marsden hospital and the Institute of Cancer Research in London. During the two years of the study, 15 women had a relapse. Researchers found tumor DNA in the blood of 12 of them as early as two weeks after surgery.Scientists previously found that small amounts of tumor DNA spills into the blood as cancer cells spread or die. Turner and colleagues tested 14 genes for cancer-causing mutations found in DNA from tumor cells but not in normal cells. But 12 of the patients didn’t have mutations in those tumor genes, making the blood test useless for them. Expanding the number of genes tested or examining all of a patient’s DNA may make the blood test useful to more people, Cristofanilli says.
Before surgery, 69 percent of the women had tumor DNA in their blood. Most of that DNA probably came from the active tumors growing in their breasts, but some may have come from cancer cells that had already started to spread. At that stage, researchers couldn’t predict which of the women would relapse.
For many of the women, removing the breast tumors cleared tumor DNA from their blood or dropped the amount below detectable levels. Researchers found that 19 percent of the women had tumor DNA in their blood two to four weeks after surgery. Cancer may have already escaped the breast and spread to other parts before those women had surgery. The presence of the tumor DNA at that early stage was a harbinger of early relapse, within about six months. One patient had circulating tumor DNA in her blood right after surgery and in follow-up samples, but scans didn’t detect a tumor within the time of the study. In other women, tumor DNA showed up later, heralding cancer’s return.
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In three women in whom the cancer had spread only to their brains, the blood test didn’t find any circulating tumor DNA. The nervous system’s blood-brain barrier probably prevents tumor DNA from leaking into the rest of the body, Turner says.
Of the women who were still cancer-free at the end of the study’s two-year monitoring period, 96 percent never had tumor DNA in their blood after surgery.
Researchers don’t know if blood tests for tumor DNA will be as effective at predicting relapse in women at low risk of breast cancer recurrence, Turner says. Breast cancer may return five to 10 years after the initial diagnosis. It’s not known whether early blood tests for tumor DNA can also foretell such long-term relapses.