A study published in the Journal of the American Medical Association shows that genetic test results, as revealed by non-invasive prenatal testing for foetal chromosome abnormalities, may detect underlying conditions in the mother, including cancer.

The study reports on a case series of eight women who had abnormal noninvasive prenatal testing results.

Their foetuses had normal chromosomes; retrospective genomic analysis showed the results were due to undiagnosed cancers in the mothers.

A team of scientists and clinicians, led by Diana W. Bianchi, MD, Executive Director of the Mother Infant Research Institute at Tufts Medical Center, reports the results of their DNA sequencing analysis in an article titled 'Noninvasive Prenatal Testing Incidentally Detects Occult Maternal Malignancies.'

Their findings demonstrate that previously undetected maternal cancers may provide a biological explanation for some prenatal screening results that differ from results of prenatal diagnostic tests.

Noninvasive prenatal screening is a recent clinical advance that provides pregnant women with information about possible chromosomal abnormalities, such as Down syndrome, in their foetuses.

The screening test, which can be offered as early as the tenth week of pregnancy, analyses fragments of placental and maternal DNA that circulate in the maternal plasma.

In women with cancer, the plasma sample also contains cancer DNA.

Diagnosis of cancer during pregnancy is relatively uncommon, with an incidence of about 1 in 1,000 women.

Cancer detected during pregnancy most often occurs in the breast, cervix, ovary and colon, as well as melanoma, lymphoma and leukaemia.

"This study provides one explanation for when noninvasive prenatal testing results are different from the fetal karyotype. It highlights the need to perform a diagnostic procedure to determine true fetal karyotype whenever noninvasive prenatal testing suggests chromosomal abnormalities," said Dr Bianchi, an international expert on noninvasive prenatal testing.

The cases in this study came from a larger group of 125,426 samples submitted from asymptomatic pregnant women who underwent noninvasive prenatal testing for foetal chromosomal abnormalities between 2012 and 2014.

Of these, 3757 cases were positive for one or more abnormalities in the number of chromosomes 13, 18, 21, X or Y.

The women's physicians later reported ten cases of cancer to the laboratory that originally conducted the noninvasive prenatal testing.

The study analysed eight of the ten cases in depth.

All of the women had abnormal noninvasive prenatal test results, and most frequently, more than one chromosomal abnormality was detected, which is a very unusual result.

Cancer was diagnosed during pregnancy or postpartum in these women at an average of 16 weeks following the initial noninvasive prenatal testing.

Some women were tested more than once, and some were tested both during pregnancy and after.

One patient had testing after treatment for colorectal cancer, and the abnormal pattern was no longer evident, suggesting a response to treatment.

"Noninvasive prenatal testing results may lead to findings of an underlying maternal condition, which, in these cases, was due to cancer," said Dr Bianchi.

"The take-home message is that women should be aware of this possibility when they seek testing. More research needs to be done to further study this occurrence to help guide physicians on how to counsel women and manage their follow-up care."

Source: Tufts Medical Center