The ovarian hormone progesterone has an important role in changing breast stem cells, according to researchers at Princess Margaret Hospital (PMH).
Published online in Nature, the study's findings are significant because reproductive history is among the strongest risk factors for breast cancer, says principal investigator Rama Khokha, a molecular biologist at Ontario Cancer Institute and the Campbell Family Cancer Research Institute, PMH. Other major known risk factors are age, genetics and breast density.
"Our study shows how and when hormones affect breast stem cells during the natural reproductive cycle. There are well accepted links between ovarian hormones and breast cancer, and there is mounting evidence that stem cells are seeds for breast cancer. We now show a direct connection between hormones and breast stem cells. "
Lead author Purna Joshi adds: "Our research demonstrates that when progesterone peaks during the second half of the menstrual cycle, it starts a cross-talk between stem cells and neighbouring cells that propels normal breast stem cells to expand in number, and may trigger an environment where cancer can begin."