How exosomes in human breast milk may influence breast cancer risk

Breast milk has a primary function to deliver nutrition to a newborn, but may also be useful to monitor the health of the lactating breast. It is known that pregnancy increases a woman’s breast cancer risk in the short term, and for women whose first pregnancy comes after age 30–35 years, for the long term. Cell-cell communication occurs in a variety of ways. A primary way for cells to communicate over distance is by the transfer of intracellular contents from one cell to another through the extracellular vesicles that cells secrete into body fluids. Exosomes are extracellular vesicles that are secreted by all cell types (with the possible exception of red blood cells) into a nearby body fluid, including milk. Exosomes provide cell-cell communication during physiologic processes such as lactation, but also in breast cancer. In this review we discuss what is known about milk exosomes, and how assessment of their contents may provide insight into the health of both the infant and the mother.