The finding comes from an analysis of clinical trial data funded by AstraZeneca, the company that makes Arimidex. AstraZeneca is a WebMD sponsor.
The study itself was performed by Walter Jonat, MD, of the University of Kiel, Germany; Michael Gnant, MD, of the University of Vienna, Austria; and colleagues.
Jonat's team combined data from three studies of postmenopausal women who, after breastcancer surgery, took tamoxifen (brand name, Nolvadex) to prevent their cancers from coming back. After two or three years of tamoxifen therapy, some of these women switched to Arimidex.
In the combined analysis, there were about 2,000 women in each group. Those who switched to Arimidex did better than those who stayed on tamoxifen:
- The Arimidex group had a 29% lower risk of death.
- The Arimidex group had a 41% higher chance of disease-free survival.
- The Arimidex group had a 45% lower chance of cancer relapse in any part of the body.
Arimidex is in a class of drugs known as nonsteroidal aromatase inhibitors. Another drug in this class, Femara, is made by Novartis. Aromasin, made by Pfizer, is a steroidal aromatase inhibitor. Novartis and Pfizer are WebMD sponsors.
These drugs block an enzyme the body uses to make estrogen, thereby suppressing estrogen levels throughout the body. After surgery, they help prevent cancer recurrence in women who have had estrogen-sensitive breast cancer.
Some women and their doctors choose to start treatment with aromatase inhibitors. Many doctors, however, start with tamoxifen and switch to aromatase inhibitors after five years.
"A lot of people have been waiting to see whether aromatase inhibitors will show a survival advantage, and I think this data will assure them that five years of tamoxifen is no longer the standard of care," Jonat said in a news release. "The best treatment for women with hormone-sensitive early-stage breast cancer should include an aromatase inhibitor."
Jonat and colleagues note that their analysis is not proof that women should switch to aromatase inhibitors after two or three years of tamoxifen. Such proof can come only from clinical trials. Such trials currently are underway.
Jonat and colleagues report their findings in the Nov. 17 online edition of The Lancet Oncology.