Arimidex and back pain??

My mother who is 77, has metastatic breast cancer..she was diagnosed in 1986, treated with surgery and Tamoxifen...she had mets to the breast bone last year treated with radiation and Arimidex...she is having elevated blood levels so her oncologist has switched her from Arimidex to IM injections of Faslodex..my question is..Can Arimidex cause back pain?? She has had bad back pain in her lower back and pain sometimes over her back hip for a few months...worse now...she is scheduled for a PET scan and bone scan...but I was wondering if back and bone pain were maybe side effects of Arimidex?? Thank you, Ilsa

[CCF-RN,MSN-JS]

Dear Ilsa, Back pain and bone pain have been reported as uncommon side effects of Arimidex (5-10%).  These are described as more generalized bone pain than specific to an area, so it make sense considering the worsening of the pain to the specific area to have it evaluated further.