Scientists Detect Breast Cancer DNA in Breast Milk

A new study found that breast milk from women with early-stage breast cancer may contain free circulating tumor DNA.

When breast cancer occurs during pregnancy or after a baby is born, the prognosis is often worse than when diagnosed during other life stages. This is because the cancer types that occur during pregnancy or postpartum tend to be more aggressive and are often diagnosed at a later stage.

However, research published on September 14 in Cancer Discovery may have found a new way to detect breast cancer earlier in women who have recently given birth.

The study was inspired by a patient diagnosed with breast cancer after pregnancy who was concerned she may have passed malignant cells to her baby by breastfeeding. Although breast milk cannot transmit breast cancer, the scientists decided to test the individual's milk frozen a year before her cancer diagnosis. The researchers found cell-free tumor DNA (ctDNA) in the sample.

To investigate further, the team collected blood samples and breast milk from individuals diagnosed with breast cancer during pregnancy or postpartum. They also collected samples from breastfeeding women without a breast cancer diagnosis.

The scientists analyzed the samples using Next Generation Sequencing (NGS) and Droplet Digital PCR (ddPCR). Among the samples, they found free circulating tumor DNA and tumor mutations in 13 of the 15 participants with breast cancer. However, the team identified ctDNA in only one blood sample.

In addition, the panel had a more than 71.4% sensitivity, meaning 7 out of 10 breast cancer cases could be detected with a specificity of 100%.

Moreover, in two participants, ctDNA was detectable in breast milk collected 18 and 6 months before diagnosis.

The researchers suggest that healthcare providers could potentially use breast milk to screen women for breast cancer after delivering a baby and during breastfeeding.

"We have shown for the first time that breast milk obtained from breast cancer patients contains sufficient ctDNA to be detected by liquid biopsy and that this ctDNA can be detected even before breast cancer can be diagnosed using conventional imaging," said corresponding author Dr. Cristina Saura from the Vall d'Hebron Institute of Oncology (VHIO), Vall d'Hebron Barcelona Hospital Campus in Barcelona, Spain.

The scientists plan to investigate the presence of breast cancer DNA in breast milk by testing 5,000 healthy women who became pregnant at 40 years or older. They also plan to include women of all ages who carry breast cancer gene mutations that increase the risk of developing the disease.