Anastrozole Arimidex benefit and side effects, breast cancer prevention
January 5 2015 by
Ray Sahelian, M.D.


Anastrozole is in a class of drugs known as non-steroidal aromatase inhibitors. When taken as a pill, it decreases the amount of estrogen the body makes. This can slow or stop the growth of many types of breast cancer cells that need estrogen to grow. The length of treatment depends on the types of prescription drugs you are taking, how well your body responds to them, and the type of cancer you have.

Anastrozole side effects, adverse reactions
Long term use of this drug is indicating that anastrozole side effects do occur with treatment of several years. Treatment for 5 years with the aromatase inhibitor anastrozole is associated with a bone loss of 6% to 7% at the lumbar spine and total hip, respectively. This was the result reported by Dr. Robert E. Coleman at the annual meeting of the American Society of Clinical Oncology. The study examines the effects of anastrozole and tamoxifen on bone health.
   Anastrozole side effect profile overall may be better than tamoxifen; however, as with all aromatase inhibitors, it is associated with a higher rate of osteoporosis and a greater incidence of fractures compared with tamoxifen. Aromatase inhibitors suppress circulating levels of estradiol, an important regulator of bone health, whereas tamoxifen, at least on bone, acts as a partial agonist.
   The ATAC sub-protocol findings are based on 81 postmenopausal women with breast cancer who took anastrozole and 86 similar women who took tamoxifen for 5 years. After 5 years, anastrozole led to a mean BMD decrease of 6% in the lumbar spine and 7% in the hip, compared with a mean decrease of 2.8% and 0.7%, respectively, with tamoxifen. Results of thee study are of concern to women who have a tendency for osteoporosis. Women treated with aromatase inhibitors may need to make sure they supplement with calcium and vitamin D supplements.


BMJ Case Rep. 2014. An unusual cause of jaundice in a patient with breast cancer. A 48-year old woman with metastatic breast cancer and extensive bone marrow infiltration was admitted with extreme lethargy, jaundice and deranged liver function tests. She had been started on anastrozole in May 2013 for bony metastases, detected on a bone scan. A CT scan performed at that time had shown no evidence of metastatic or nodal disease elsewhere. Over the subsequent 2 months, the patient had become progressively jaundiced. Outpatient abdominal ultrasound and CT liver had shown a fatty liver with no focal lesions. She was admitted in August 2013 with bilirubin 567, alkaline phosphatase 385, alanine aminotransferase 98, albumin 25 and international normalised ratio 1.9. The patient ultimately had a liver biopsy, which demonstrated features of drug-induced steatohepatitis, and anastrozole was found to have been the probable cause.

Anastrozole for breast cancer
Tamoxifen or anastrozole may be given as adjuvant treatment to women with early-stage breast cancer to reduce the risk of cancer recurrence. Mature data from the ATAC (Arimidex, Tamoxifen, Alone or in Combination) trial, reported in The Lancet  in 2005 showed that 5 years of anastrozole is more effective in preventing breast cancer recurrence than 5 years of adjuvant tamoxifen.


Lancet. December 2013. Anastrozole for prevention of breast cancer in high-risk postmenopausal women (IBIS-II): an international, double-blind, randomised placebo-controlled trial. Aromatase inhibitors effectively prevent breast cancer recurrence and development of new contralateral tumours in postmenopausal women. We assessed the efficacy and safety of the aromatase inhibitor anastrozole for prevention of breast cancer in postmenopausal women who are at high risk of the disease. Between 2003, and 2012, we recruited postmenopausal women aged 40-70 years from 18 countries into an international, double-blind, randomised placebo-controlled trial. To be eligible, women had to be at increased risk of breast cancer (judged on the basis of specific criteria). Eligible women were randomly assigned (1:1) by central computer allocation to receive 1 mg oral anastrozole or matching placebo every day for 5 years. Randomisation was stratified by country and was done with blocks (size six, eight, or ten). All trial personnel, participants, and clinicians were masked to treatment allocation; only the trial statistician was unmasked. The primary endpoint was histologically confirmed breast cancer (invasive cancers or non-invasive ductal carcinoma in situ). Analyses were done by intention to treat. 1920 women were randomly assigned to receive anastrozole and 1944 to placebo. After a median follow-up of 50 years 40 women in the anastrozole group (2%) and 85 in the placebo group (4%) had developed breast cancer. The predicted cumulative incidence of all breast cancers after 7 years was 56% in the placebo group and 28% in the anastrozole group. 18 deaths were reported in the anastrozole group and 17 in the placebo group, and no specific causes were more common in one group than the othe. Anastrozole effectively reduces incidence of breast cancer in high-risk postmenopausal women. This finding, along with the fact that most of the side-effects associated with oestrogen deprivation were not attributable to treatment, provides support for the use of anastrozole in postmenopausal women at high risk of breast cancer.