The reason behind the aggressiveness and frequency of pregnancy-associated breast cancer has been explained in a claim made by researchers at the University of Illinois at Chicago.
According to the new research, expression of inflammatory-related genes in breast tissue of women who have previously given birth may be behind the crime.
Pregnancy at a relatively young age reduces the risk of breast cancer over the long term, but epidemiological studies have found that women are at an increased risk for breast cancer during pregnancy and for up to 10 years after giving birth, said Debra Tonetti, associate professor of pharmacology and lead researcher on the study.
She added that these pregnancy-associated breast cancers also carry an unusually high risk of spreading to nearby organs and for lethality as compared to breast cancers in women who have never been pregnant.
To reach the conclusion, Tonetti and her research team examined the level of expression of 64 genes in tissue from benign breast biopsies and breast-reduction surgeries at the University of Illinois Medical Center at Chicago.
The women, who were between the ages of 18 and 45, were divided into three categories: those who had never been pregnant, those who had been pregnant within the past two years, and those who had been pregnant five to 10 years previously.
The set of examined genes included genes known to be related to immunity and inflammation, extracellular matrix remodeling, angiogenesis (the growth of new blood vessels vital to wound healing) or hormone signaling.
Twenty-two percent of the examined genes showed significant difference in expression in the breast tissue of women who had never given birth compared with those who had. Inflammation-related genes, as a class, were more active in women who had borne a child. Involution-the process by which the breast returns to normal following lactation-could be a cause of the inflammation, she said.
"Our results showed an increase in immune/inflammatory activity in the post-pregnant breast," Tonetti said. "Interestingly, this response was not limited to the recently pregnant group, but also characterized more distant pregnancies as well."
A surprising finding was evidence of a protective effect of pregnancy as well, since the expression of many hormone and growth factor signaling genes suggests protection. These findings indicate that a balance between high risk inflammatory and protective hormone signaling gene expression may ultimately determine a woman's individual breast cancer risk, she said.