el cubano
You obviously know your stuff but I'll point out 2 things:
1.) Men don't have an endometrium and so can't contract endometrial cancer.
2.) FDA approval for the use of tamoxifen in breast ca was back in the 90's, since then the use of tamoxifen has become 1st line treatment for breast CA (apart from surgery) and is extensively used also for palliative care.
It's interesting that tamoxifen isn't curative for gyno though. Would people recommending taking it prophylactically? and not wait for symptoms.