A new study has reported that women who have given birth experience changes in gene expression in their breast tissue that reduce the risk of breast cancer in the long term. Previous population studies have reported that pregnancy results in a short period of elevated risk of breast cancer followed by a long-term period of protection. In the study, the expression of a customized gene set was assessed in normal breast tissue from nulliparous (never having given birth), recently pregnant (within two years of pregnancy), and distantly pregnant (five to 10 years since pregnancy) age-matched premenopausal women. The genes investigated included breast cancer biomarkers and genes related to hormone signaling, extracellular matrix remodeling, angiogenesis, and immune/inflammation.

Fourteen of 64 (22%) of the selected genes were found to be differentially regulated in breast tissues from nulliparous women compared to samples from women who had ever given birth (whether recently or five or more years previously). Inflammation-associated genes were found to be significantly upregulated as a group in both groups of women who had given birth compared to women who had never given birth. In addition, women who had ever given birth had significantly lower expression of estrogen receptor α, progesterone receptor, and ERBB2 (Her2/neu), as well as two-fold higher estrogen receptor β expression compared with non-mothers. The authors comment that these initial findings, among the first on gene expression in normal human breast tissue, provide clues about the mechanisms behind the time-dependent effects of pregnancy on breast cancer risk.