In humans having a child before the age of 20 decreases risk of breast cancer by half.
Using microarray analysis researchers from Basel discovered that genes involved in the immune system and differentiation were up-regulated after pregnancy while the activity of genes coding for growth factors was reduced.
The activity of one particular gene Wnt4 was also down-regulated after pregnancy.
The protein from this gene (Wnt4) is a feminising protein - absence of this protein propels a foetus towards developing as a boy.
Wnt and Notch are opposing components of a system which controls cellular fate within an organism and when the team looked at Notch they found that genes regulated by notch were up-regulated, Notch-stimulating proteins up-regulated and Notch-inhibiting proteins down-regulated.
Wnt/Notch signalling ratio was permanently altered in the basal stem/progenitor cells of mammary tissue of mice by pregnancy.
Mohamed Bentires-Alj from the Friedrich Miescher Institute for Biomedical Research, who led this study said, "The down-regulation of Wnt is the opposite of that seen in many cancers, and this tightened control of Wnt/Notch after pregnancy may be preventing the runaway growth present in cancer."
The research is published in the open access journal Breast Cancer Research.