Hi there and thanks for sharing your question with us on HCM. Tamoxifen is a non-steroidal anti-estrogen drug. It is approved for the treatment of breast cancer. Unfortunately, it acts as an agonist in the uterus, and can cause thickening of the endometrium. This thickening can lead to the formation of benign fibroids. However,there is also a small risk of endometrial cancer in some women. The cumulative risk of developing endometrial cancer using tamoxifen is 1.6% at 5 years and 3.1% if use for 5 - 14 years. However, the benefits of using Tamoxifen to treat breast cancer outweigh the side effects and risks of developing endometrial cancer. Also, should endometrial cancer develop, it can be quickly identified early and treatment is curative. As the risk of women developing endometrial cancer is low, there is no generalized screening protocol and each patient is handled on a case to case basis. I am glad that you have had an endometrial biopsy done. I think your symptoms suggest that the tamoxifen has caused your uterus to thicken again and cause you cramps and spotting. You will have to watch your symptoms closely and attend follow up regularly. Some women are put on an levornogestrel intrauterine system ((LNG IUS) to reduce the risk of polyps and endometrial hyperplasia. However the LNG IUS can cause abnormal vaginal bleeding and the risk for breast cancer recurrence while on this IUS is uncertain. You could take an anti spasmodic painkiller like mefenamic acid to cope with the pain caused by the cramps. Regular intake of good omega 3 like a good quality fish oil may help alleviate the severity of the cramps. The omega 3 will also have other benefits for your health. I hope this advice helps. Thank you.