Tamox to be used in high risk women to PREVENT bc?

It has been used in this way, as a preventative for high risk women, in the U.S. for several years.

Per WebMD:

"Women who have no history of breast cancer can take tamoxifen as a way to protect them from getting the disease. This drug reduces the risk of breast cancer in two ways:

1. It blocks estrogen from working on cancer cells that are sensitive to the hormone. (this action would slow down any existing cancer)
2. It blocks estrogen from acting on cells that are not cancerous. ( this action is to prevent cancer from happening)

Tamoxifen also keeps healthy breast cells from growing and multiplying. That way, it also reduces the number of cells that could become cancer." (also a way to prevent cancer from happening)

So while it doesn't "kill" cancer cells it can prevent cells from becoming cancerous in the first place. Also why women who've had BC before are given it to prevent a new BC. Some studies do seem to show it may have a cancer killing effect by basically putting cancer cells to sleep, perhaps permanently. Despite the fact Tamoxifen has been around for many years, lots of articles, including the one on WebMD say, 'Scientists aren't sure exactly how the drug works" only that it does seem to work for some women some of the time.