If this drug had absolutely no side effects and yet did what it did in terms of reducing the number of invasive breast cancer, I believe almost everyone would take the drug. It's that simle. But unfortunately, there are very few drugs viable these days that have no side effects. In addition to the uterine cancer issue, the women who took tamoxifen had a higher incidence of thromboembolic disorders, that is, developing clots that in some isntances, three cases, led to the death of the individual taking that drug. Now, three women out of 6,000 or so is a small number to be sure.
Uterine cancer is a very treatable and often curable cancer but it can also be a fatal cancer.
It's not an easy cancer to detect. And similary with the other side effects. So it is not trading off as somebody said one disease for another, that just doesn't exist. The choice will vary depending on a woman's age, personal history, family history, and how she weighs the benefits and risks. In other words, if I was a woman with high risk breast cancer I would still think that this is a good idea.