Researchers have discovered that breast myoepithelium cells actively work to keep breast cancer cells from spreading throughout the body. The findings were reported in the Journal of Cell Biology.

Most breast cancers develop in the cells that line the inside of breast milk ducts. Myoepithelium cells, which are normally used to contract and move milk through the ducts when a woman is breastfeeding, surround the cancer cells and create a protective barrier to keep them from spreading. But not merely serving as a stationary wall, myoepithelium cells actively reach out and “grab” cancer cells that are trying to break through the barrier. 

Researchers tested the behavior in engineered mouse cells. When the cancer cells broke through the myoepithelium, the body pulled them back into the breast lining 92% of the time. When the researchers manipulated the proportion of myoepithelial cells to increase them to two per each cancer cell, the escape rate decreased fourfold. 

The study authors said that the findings may one day be used to predict which people may be more likely to develop invasive or metastatic breast cancer.