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Expecting mothers typically opt for prenatal genetic testing during their first and third trimesters. Performed with a sample of the mother’s blood, this test looks for fetal aneuploidy, an abnormal number of chromosomes. Though the test is already valuable for its ability to predict nonviable pregnancies and developmental disorders, it’s accidentally become useful for another purpose: spotting “hidden” cancer.
The non-invasive test’s second use first came to light in 2013, when a seemingly healthy 37-year-old mother had her fetus tested for fetal aneuploidy. The results revealed that her fetus possessed only one copy of chromosome 18 and an extra copy of chromosome 13, the latter of which points to Patau syndrome, a life-threatening condition rife with developmental and health issues. Further investigation suggested the results of the test were incorrect, so the mother went on to carry her otherwise uneventful pregnancy to term. When she gave birth, her baby was deemed perfectly healthy.
After giving birth, however, the mother began to complain of “persistent and worsening” pelvic pain. MRI scans revealed multiple lesions, which were then tested via fine needle aspiration, in which a thin needle is used to extract cells from a specific part of the body. The lesions turned out to be tumors, which shockingly lacked a copy of chromosome 18 and possessed an extra copy of chromosome 13—the same abnormality suggested early in the woman’s pregnancy. The woman was diagnosed with metastatic small cell carcinoma of vaginal origin—a highly aggressive form of vaginal cancer which, in her case, proved fatal.
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Since then, scientists have wondered whether the standard prenatal blood test might reliably serve a dual purpose. Cancers tend to shed DNA into the bloodstream, which is why many medical research labs and startups—including the failed Theranos—have attempted to produce an effective cancer-detecting blood test. To see whether prenatal testing could spot other forms of cancer during pregnancy, researchers at the National Institutes of Health (NIH) recruited people who had received “unusual” or “nonreportable” fetal aneuploidy results, then used additional methods to screen them for cancer.
Of the 107 participants, 52 had some form of cancer, as revealed by further testing. Thirty-one of the people with cancer had lymphoma, a form of blood cancer, while 20 participants had tumors. These tumors sat all over the body, from the bile duct, breast, and colon to the kidney, lung, and pancreas. More than half of the participants experienced zero symptoms of disease, meaning they would have assumed they were healthy if not for their abnormal prenatal test results. Another 10 participants experienced symptoms but either ignored them or were shrugged off in a medical setting.
But what about the 55 participants who didn’t have cancer? Of those, 30 were shown to have other health conditions that could trigger strange test results, like fibroids or actual issues with the fetus. Other participants’ odd results couldn’t be blamed on anything apparent, so they’re being observed for the next five years.
The NIH researchers hope that their work will not only help in the development of blood-based cancer tests, but also encourage the use of broader health screenings for pregnant individuals. Of the post-prenatal testing methods used, whole-body MRI was most effective at identifying potentially life-threatening conditions. But that’s not an imaging option most health insurance policies cover, nor is it something obstetricians tend to order.