Rx Cut Breast Cancer Incidence in Older Women in Half

Arimadex significantly reduced first time breast cancer in high risk postmenopausal women

/ Author:  / Reviewed by: Joseph V. Madia, MD Beth Bolt, RPh

(RxWiki News) For years, postmenopausal breast cancer survivors have been treated with medications that block estrogen production to reduce the risk of cancer returning. One medication may also prevent the disease from developing at all.

Arimidex (anastrozole) was found to reduce the incidence of breast cancer in high risk postmenopausal women by more than 50 percent.

The authors of this study suggested that while additional research is needed, it appears that Arimidex may be an ideal preventive therapy for postmenopausal women who have elevated breast cancer risks due to a family history of the disease.

"Discuss breast cancer prevention with your doctor."

The lead investigator of this trial — the IBIS-II Prevention Study — was Jack Cuzick, PhD, head of the Cancer Research UK Centre for Cancer Prevention and director of the Wolfson Institute of Preventive Medicine at Queen Mary University of London.

Arimidex belongs to a class of medications called aromatase inhibitors, which block the body’s ability to produce estrogen, the female hormone that fuels 80 percent of breast cancers. These are estrogen receptor-positive (ER+) breast cancers.

The medication has traditionally been given to postmenopausal women following primary treatment to reduce the risks of the cancer returning (recurrence).

Dr. Cuzick and team sought to learn if Arimidex could also be effective in preventing the disease in high risk postmenopausal women. Women at high risk of breast cancer have one or more of the following risk factors:

  • Two or more blood relatives who have had breast cancer
  • Mother or sister who developed breast cancer before the age of 50
  • Mother or sister who had breast cancer in both breasts

For this study, a randomized, placebo-controlled trial, 3,864 postmenopausal women with no personal history of breast cancer were recruited between 2003 and 2012. Participants were randomly assigned to one of two groups: 1,920 participants received 1 mg of Arimidex daily, and 1,944 women in the study were given a placebo (sugar pill). The median age of participants was 59.3.

After five years of follow-up, 125 breast cancers were diagnosed. The researchers discovered that compared to those who were given a placebo, the women who received Arimdex had:

  • A 53 percent lower incidence of breast cancer.
  • A small increase in fractures — 8.5 percent versus 7.7 percent.
  • A 10 percent increase in adverse musculoskeletal events such as joint pain and carpal tunnel syndrome.

Interestingly and unexpectedly, the investigators found that the women taking Arimidex had a lower level of other cancers compared to the women taking placebo, including about half the number of skin cancers (14 versus 27), a third fewer cancers of the gastrointestinal tract (4 versus 12) and about 25 percent fewer gynecologic cancers (8 versus 12).

“Our initial results show that for postmenopausal women who do not have breast cancer, but are at high risk for developing the disease, anastrozole reduced breast cancer incidence by 53 percent with very few side effects,” Dr. Cuzick said in a statement.

Two other antihormone therapies — tamoxifen (sold under a variety of brand names including Nolvadex and Soltamox) and raloxifene (sold under the brand name Evista) — are also used as breast cancer preventive therapies. But, according to Dr. Cuzick, “these drugs are not as effective and can have adverse side effects, which limit their use.”

Participants in the IBIS-II Prevention study will be followed for at least an additional 10 years. "We want to determine if anastrozole has a continued impact on cancer incidence even after stopping treatment, if it reduces deaths from breast cancer, and to ensure that there are no long-term adverse side effects.”

Findings from this study were presented at the 2013 San Antonio Breast Cancer Symposium and simultaneously published in The Lancet.

AstraZeneca, the maker of Arimidex, funded the research. Several of the authors reported ties with the company and other pharmaceutical firms.

Review Date: 
December 12, 2013
Last Updated:
December 12, 2013