This thesis explores the relationship between tamoxifen treatment in breast cancer and the risk of developing tamoxifen-induced endometrial cancer. Tamoxifen is a selective estrogen receptor modulator, meaning it acts as an estrogen antagonist in some tissues as well as an estrogen agonist in others. It acts as an estrogen antagonist in breast cancer tissue but as an estrogen agonist in endometrial tissue. Research has shown a significant increase in the risk of developing endometrial cancer in patients being treated with tamoxifen. The risk-benefit ratio is explored as well as alternative and upcoming methods of breast cancer treatment.