HRT Linked To Breast Cancer

A scientific breakthrough has identified a key signal that acts as a trigger for the growth of breast stem cells. This new finding helps researchers gain a better understanding of the mechanism for the development of breast cancer. The results of this work are to be reported in an issue of Nature.

Exciting News

Associate Professor Jane Visvader and a team of colleagues at the Melbourne-based Walter and Eliza Hall Institute of Medical Research (WEHI) are responsible for this important finding. Coauthor of the study Geoffrey Lindeman found it difficult to contain his enthusiasm, "What's exciting is that it helps spotlight some of the mechanisms that may be involved in very early stages of breast cancer," he said.

Lindeman explains that in identifying these signals, researchers get a better idea of what treatments might be effective for or even prevent breast cancer.

Both progesterone and estrogen, the female hormones, play a role in the development of healthy breasts as well as in the development of breast cancer. However, researchers have seen that a greater exposure to these hormones, for instance through starting to menstruate at an early age, being pregnant, reaching menopause later, or using hormone replacement therapy (HRT) result in an increased risk for breast cancer.

Likely Choice

Lindeman, also an associate professor at WEHI said that until this study, researchers hadn't known for sure which cells were implicated in breast cancer, but that breast stem cells had been thought to be a likely choice since they have the gift of longevity which would give them the time to develop the mutations that have been linked with cancer. But Lindeman and Visvader had earlier discovered that the breast stem cells of mice and humans don't contain receptors for estrogen and progesterone.

In this new study, Dr. Marie-Liesse Asselin-Labat, a post-doctoral researcher, performed lab research on mouse mammary stem cells (MaSC's) which Lindeman says look a great deal like their human counterparts. Asselin-Labat discovered that MaSC's have a strong response to the signals of steroid hormones. "Despite lacking the sensors [for estrogen and progesterone], the stem cell is exquisitely sensitive to hormone manipulation," he said.

Chemical Signal

In the course of this study, pregnancy and estrogen and progesterone treatment both served to increase the number of MaSC's but there was a decrease after removal of the ovaries was performed or anti-estrogen treatments were administered. Lindeman says one major finding in this study was that the cells that line breast ducts act as a go-between for hormones and stem cells. These breast duct cells have both progesterone and estrogen sensors so respond to these hormones by giving off a chemical signal known as RANK that gives instructions to the MaSC's."There seems to be this cross-talk or conversation that goes on between hormone-sensor-positive cells in the breast and the stem cells," he said.

Lindeman states that these findings will help researchers exploring drug treatments for the treatment and prevention of breast cancer.

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