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Prenatal Testing Sometimes Detects Cancer in Mothers

When Marin Mejia got pregnant at age thirty-nine, she had a test to screen her fetus for genetic abnormalities. The baby was fine. Mejia had cancer. The test found DNA fragments in her blood that came from a tumor.

Sophisticated, noninvasive prenatal testing, like the kind Mejia received, “picks up very unexpected things”—including imbalances in the genome of mothers that may be associated with a tumor, says Diana W. Bianchi, the Natalie V. Zucker Professor of Pediatrics, Obstetrics, and Gynecology at Tufts School of Medicine. For a paper published in the Journal of the American Medical Association in June, Bianchi and her research team analyzed the noninvasive tests of 125,426 women who had abnormal results but delivered healthy babies. Ten of the women had been diagnosed with cancer after the tests.

Unlike amniocentesis—an invasive screening that samples the fluids around a fetus for genetic material—noninvasive tests analyze the fetal genome by sequencing DNA fragments floating in the mother’s blood. As a fetus develops, some placenta cells die and release fragments of the baby’s DNA into the mother’s bloodstream. By the tenth week of pregnancy, says Bianchi, fetal DNA makes up as much as ten percent of the DNA fragments in a mother’s bloodstream.

The noninvasive test does turn up the occasional false-positive result, “but we didn’t know that tumors could be a cause until 2013,” Bianchi says. That was when a case report crossed her desk for a professional journal she edits, Prenatal Diagnosis, about a mother whose test showed a false-positive result for two chromosomal abnormalities. Shortly after giving birth to a healthy son, the woman was diagnosed with cervical cancer.

Bianchi, who is also executive director of the Mother Infant Research Institute at Tufts Medical Center, and her colleagues at Illumina—one biotech company that manufactures the genetic screening test—began asking doctors to report such cases. “The biggest red flag was the presence of more than one chromosomal abnormality,” Bianchi says, because if a fetus has more than one, it probably wouldn’t survive.

In a commentary in the journal Nature, Bianchi recommended that consent forms be revised to indicate that the tests could also signal health issues in mothers. “It’s a problem because some women are terminating their pregnancies without realizing the abnormal result could be from their own DNA,” she says.

Marin Mejia’s tests revealed four chromosomal abnormalities. She was diagnosed with anal cancer; her son, Owen, was born healthy.

Bianchi stresses that the test will never be used as a cancer screen. “We detected the multiple chromosome abnormal results in 39 women out of 125,426, so it’s an extremely rare finding,” she says. “Of those, we know of only ten who have had cancer.”

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