Our UHN programs and services are among the most advanced in the world. We have grouped our physicians, staff, services and resources into 10 medical programs to meet the needs of our patients and help us make the most of our resources.
University Health Network is a health care and medical research organization in Toronto, Ontario, Canada. The scope of research and complexity of cases at UHN has made us a national and international source for discovery, education and patient care.
Our 10 medical programs are spread across eight hospital sites – Princess Margaret, Toronto General, Toronto Rehab’s five sites, Toronto Western – as well as our education programs through the Michener Institute of Education at UHN. Learn more about the services, programs and amenities offered at each location.
Maps & Directions
Find out how to get to and around our nine locations — floor plans, parking, public transit, accessibility services, and shuttle information.
Ways You Can Help
Being touched by illness affects us in different ways. Many people want to give back to the community and help others. At UHN, we welcome your contribution and offer different ways you can help so you can find one that suits you.
The Newsroom is the source for media looking for information about UHN or trying to connect with one of our experts for an interview. It’s also the place to find UHN media policies and catch up on our news stories, videos, media releases, podcasts and more.
Cancer researchers at Princess Margaret Hospital (PMH) have discovered that the ovarian hormone progesterone plays a pivotal role in altering breast stem cells, a finding that has important implications for breast cancer risk.
The findings, published online today in Nature(10.1038/nature09091;http://dx.doi.org/), 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".
Until now, breast stem cells were thought to be generally inactive in the adult female breast, says Dr. Khokha, whose speciality is modelling human cancer in the laboratory. In this study, the research team replicated the human natural reproductive cycle in mice to determine the impact of hormones on breast stem cells.
How hormones change these stem cells opens a new pathway to understanding the cell growth that begins breast cancer, and, with further research, will open new ways of targeting stem cells.
"It is the first evidence, to our knowledge, for progesterone-driven dynamic shifts in the mammary stem cell pool. This activation provides an opportunity to start the process of cell transformation leading to breast cancer."
The research was also supported by the Canadian Cancer Society Research Institute and the Canadian Breast Cancer Foundation.