I think it is a no-no, as herbs, etc. like soy, black cohosh are.  I feel
for you, just call me old sweaty head.

Estroven claims to contain soy phytoestrogens, this appears to be the
relevant ingredient.

I don't think there is any evidence that soy increases the risk of a
primary cancer occurring, what evidence there is seems to point both
ways, but there is a suspicion that it may increase the risk of a
recurrence in patients who have had a cancer.

So the advice is that these patients should avoid soy based supplements
or a diet containing  large amount of soy, although the amount of soy
found in processed foods etc. in a 'normal' western diet is probably
harmless.

I don't think I've ever heard anyone say that someone who is at high
risk for breast cancer but has not actually had it, should avoid soy.
But I don't suppose anyone really knows.

Tim Jackson