Yes, this is the consensus of the studies I have read and also what was reported to me by my oncologist. Easily, there is a 30-50% reduction in recurrance of Estrogen Positive breast cancers (those that would be inhibited by the AI that inhibits Estrogen production, so the hormone not as available to trigger growth of any rogue cells with the Estrogen receptor and would therefore trigger growth). It is easy to find these studies with a google search (beware of the site as reputable)

I am on Exemestane (a steroid AI, one month) after trying the AI called anastrozole for 5 months. I had almost all of the negative side effects with anastrozole, so oncologist said let's try another. It is worth pressing on to find the right one, I figure going from an average 10% recurrance to 5% is worth it. Press on, we can do this.