Researchers in this study wanted to understand why early pregnancy lowers a woman’s risk of developing breast cancer later in life. Previous studies have shown that women who have a full-term pregnancy at a younger age often have a reduced risk of breast cancer, but the biological reasons behind this protective effect were not fully understood.
To investigate this, the researchers analyzed normal breast tissue samples from several groups of women, including those who had never given birth (nulliparous), women who had experienced pregnancy (parous), and women carrying BRCA1 or BRCA2 genetic mutations, which are linked to a higher risk of breast cancer. They examined gene activity and molecular changes in different types of breast cells to identify differences between these groups.
The researchers discovered that pregnancy appears to change certain breast cell populations—particularly progenitor cells, which are early-stage cells capable of developing into other breast cell types. In women who had given birth, these progenitor cells showed lower activity in genes linked to stem cell growth and cell division, including genes involved in pathways such as IGF, TGF-β, and Hedgehog signaling. They also found fewer cells expressing the protein p27, which is associated with cell growth regulation.
These results suggest that pregnancy may reduce the number or activity of certain breast cell types that could otherwise develop into cancer, helping explain why early pregnancy provides long-term protection against breast cancer.
