I've often wondered if the rumours I've heard about soy foods causing cancer are true or not. So I checked Google Scholar, and apparently the rumours are false. Or, as of 1994, this paper couldn't find any papers find a positive correlation between soy intake and cancer, and 65% of the papers they looked at found that soy products reduced tumor formation.

Soy intake and cancer risk: a review of the in vitro and in vivo data

But I also found this paper. It suggests that soy supplements might not have any positive influence on symptoms of menopause, even though I think they're used a lot.

The effects of soy protein containing phytoestrogens on menopausal symptoms in postmenopausal women