Prenatal genetic tests spot 'hidden' cancer in mothers

A blood test that screens for fetal disorders during pregnancy also accurately signposts cancers in unsuspecting mothers-to-be.

A small study led by the National Institute of Health in Maryland, investigated pregnant and postpartum women who had received unusual cell-free DNA (cfDNA) results during their pregnancy but had fetal abnormalities ruled out. Despite none of the women outwardly displaying any signs, nearly half of the women were diagnosed with cancer.

'They looked like healthy, young women and they reported themselves as being healthy,' said Dr Diana Bianchi, director of the Eunice Kennedy Shriver National Institute of Child Health and Human Development, and lead author of the study published in the New England Journal of Medicine.

cfDNA blood tests are commonly used to check for fatal genetic disorders in the developing fetus. During pregnancy, the placenta – which shares the same genetic code as the fetus – sheds DNA into the mother's bloodstream. Similarly, cancerous tumours can shed DNA into the bloodstream too.

Using MRI scanning, the researchers found that of the 107 women enrolled, 52 (48.6 percent) had 'hidden' cancers – most commonly lymphomas, followed by bowel and breast cancers. The majority had no signs of their disease, while others had symptoms that were deemed to be pregnancy-related.

Of the 55 women without cancer, 30 had non-cancerous reasons that explained their cfDNA results (most commonly fibroids), 15 had false positives, and 10 remain unexplained.

It is believed that one in 10,000 cfDNA tests return an unusual result, around 250 people in the USA each year, however further investigation is required to distinguish between fetal abnormalities or cancer.

'They and their care providers need to take the results seriously and have additional testing because in that population there is a 48 percent risk of cancer,' added Dr Bianchi.

When further scans and tests exclude fetal abnormalities, the researchers claim that whole-body MRIs are required to rule out cancer. They hope the study will urge more pregnant people to undertake cfDNA testing, as many expectant parents turn down such tests due to fears of high rates of false positives.

In an accompanying editorial, Dr Neeta Vora, cfDNA expert and director of reproductive genetics at the University of North Carolina at Chapel Hill, said, 'we still have a long way to go to improve provider education regarding the possibility of identifying maternal cancer through cfDNA screening, as well as to improve laboratory standardisation, reporting of suspicious findings, and access to imaging methods such as whole-body MRI.'