Hello, and I would be happy to answer your question today. It is true that Tamoxifen can cause your uterine lining to appear thick on an ultrasound, but the endometrium can measure even up to 2cm in thickness close to the time your period is due to come in normal, healthy menstruating women. So if you still menstruate, there is no reason to suspect that your uterine lining is thick due to any form of hyperplasia or cancer. I also agree with your doctor that there is no way that the tamoxifen could have given you uterine cancer in such a short period of time. The wording of radiology reports can be scary sometimes, because they do not know your medical history. When they see a thickened endometrium in a patient on Tamoxifen, they recommend ruling out hyperplasia or cancer because they are concerned about medical liability if cancer is missed. I recommend you consult your GYN doctor for advice on this matter. They probably will recommend you have a procedure called and endometrial biopsy, which is performed in a gynecologist s office. A narrow straw is inserted into the uterus to suck out a small amount of tissue to be analyzed for the presence of hyperplasia or cancer. Again, I think it is EXTREMELY UNLIKELY you have cancer, however, most GYN doctors would recommend getting the biopsy to be safe. If the biopsy just shows menstrual tissue, there is no further evaluation necessary unless your symptoms change. So in summary- I agree with your oncologist that the tamoxifen should have not had an effect on your uterine lining that quickly and also that the thickness of your uterine lining on this ultrasound exam is normal for the time of your menstrual cycle. It is likely, however, that your GYN would most likely recommend an endometrial biopsy to rule out hyperplasia or cancer anyway because of the wording of your report. In the meantime, concentrate on healing from your surgery and I hope the information I gave you was reassuring. Best wishes, Dr. Brown