Abnormal results on noninvasive, prenatal genetic tests don't always indicate a problem with the foetus. In some cases, these tests may uncover maternal cancers, a new study reports.
"If the test comes back abnormal, the patient should not panic," said study researcher Dr. Diana Bianchi, executive director of the Mother Infant Research Institute at Tufts Medical Centre in Boston. "It doesn't necessarily mean anything is wrong with the foetus."
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In her study, 10 women had abnormal findings on a noninvasive prenatal test. A more invasive follow-up test found normal results for the foetus, but the test also revealed cancer in the mother.
The findings, Bianchi said, point to the need to do further tests if the noninvasive blood test comes back positive. The chances of this happening are low, she said, but it's crucial to consider the possibility.
"Cancer is not that common in pregnant women," Bianchi said. "It [affects] about one in 1,000."
While the cancer diagnosis is not welcome news either, getting the abnormal test result initially may result in an earlier diagnosis and a better prognosis for a woman with cancer, the authors said.
Analysis of mother's blood
The study is published in the July online edition of the Journal of the American Medical Association. Funding for the study was provided by Illumina, a company that makes a noninvasive prenatal test (NIPT). Bianchi is a member of an advisory panel for Illumina.
Noninvasive prenatal testing is a screening test that has become widely available in the last four years or so, Bianchi said. It is a screening test that analyses the mother's blood, which contains fragments of both placental and maternal DNA.
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The test looks for certain foetal abnormalities associated with specific chromosomes that may indicate birth defects or a condition, such as Down's syndrome, according to background information in the study.
NIPT can be done as early as the 10th week of pregnancy and is typically offered to women with high-risk pregnancies, such as older mothers or those with a family history of certain birth defects such as Down's syndrome, according to the American College of Obstetricians and Gynaecologists.
In women with cancer, the blood sample from NIPT will also contain cancer DNA. "If someone has cancer, the tumour itself is shedding DNA in the mother's blood," Bianchi said. "The test is picking up excess amounts of DNA from particular chromosomes. It's kind of an accident in a way that the test is picking up the DNA from the tumour."
For the study, Bianchi looked at more than 125,000 samples from women who had NIPT between 2012 and 2014. Of that number, more than 3,700 had positive results for one or more abnormalities in five different chromosomes linked with birth defects. Later, 10 of these women were diagnosed with cancer, the study found.
Small chance of cancer
The more foetal abnormalities the test picked up, the greater the likelihood that the pregnant woman had cancer, Bianchi found. Normally, the test may pick up one abnormality, she said.
"But seven of the 10 women had more than one," which is unusual. "If it's just a single abnormality, it's much less likely to be cancer," she said.
The chance that the abnormal NIPT result is due to cancer is small, said Dr. Roberto Romero, chief of the perinatology research branch at the U.S. National Institute of Child Health and Human Development of the National Institutes of Health. He reviewed the findings and wrote an editorial to accompany the study.
For women, the bottom line is that if the results of the blood test come back abnormal, they should next have a diagnostic test, such as amniocentesis, according to Romero.
"An important message is that the NIPT is not a screening test for cancer during the pregnancy," he said.
Women should be made aware of the possibility of this result when they undergo the NIPT, Bianchi said. If the test comes back abnormal, they need a follow-up diagnostic test, she agreed.
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