The increase in the over 50 year old group was staggering. It was about 4.5 times more likely in the Tamoxifen group. If it turns out there was randon bias in the control group, then the increases could be even worse. Taking Tamoxifen preventively simply trades one disease for another, one cause of death for another. The disease a woman trades for may be worse beyond the absolute numbers.
Blood clots can cause immediate death and permanent disability.
With breast cancer there is the possiblity of cure or at more years of life. The models used to assess predict high risk for breast cancer are not well developed. Worse yet, when they do pick up high risk breast cancer they are also picking up those at high risk for endometrial cancer. It is also known that minority women were not well represented in this study, in spite of efforts to do so. So whatever the final results may be, they may not apply to all women.