I am 57 years of age and had breast cancer 3 years ago. I have been taking Arimidex since the breast cancer prior to that I was taking HRT. Since stopping HRT I haven't had a period but had one that lasted 7 days a couple of months ago. I asked my GP if this was a side effect of Arimidex and was sent for a hysteroscopy and the results show I have atrophic endometrium. Can you explain what this is pleasae? Thankyou