Low Breast Cancer Pill Use Ups Death

Sept. 6, 2007 -- Women who fail to take the breast cancer drug tamoxifen as prescribed may be placing themselves at substantially increased risk of dying, a study of more than 2,000 women shows.

"Our most significant finding was that women who filled 70% or fewer of their tamoxifen prescriptions had a significantly -- 16% -- increased risk of death [compared with women who filled all their prescriptions]," says Alastair Thompson, MD, professor of surgical oncology at the University of Dundee in Scotland and one of the researchers.

In the study, one in 10 women filled 70% or fewer of their tamoxifen prescriptions, he tells WebMD.

Refills are a well-accepted surrogate for how many pills a person actually takes, as it is rare for people to buy medication if they still have some left.

The research is being presented here this week at the 2007 Breast Cancer Symposium, co-sponsored by the American Society of Clinical Oncology and four other cancer care groups.

Findings Apply to Newer Hormone Drugs, Too

Doctors have been using tamoxifen to fight tumor growth in women with breast cancer who have tumors that are fueled by estrogen for over 25 years.

More recently, newer hormone drugs known as aromatase inhibitors, such as Aromasin, Arimidex, or Femara, have been shown to shrink tumors better, with fewer side effects.

While tamoxifen deprives breast cancer cells of the estrogen they need to grow, aromatase inhibitors actually block an enzyme needed to make estrogen, thereby slashing the body's production of estrogen altogether.

Nonetheless, tamoxifen still has an important role in breast cancer treatment, says Julie R. Gralow, MD, an associate professor of medical oncology at the University of Washington School of Medicine in Seattle, and moderator of a press briefing on the findings.

Aromatase inhibitors can only be given to postmenopausal women, leaving tamoxifen as the cornerstone of hormone therapy in younger women, she points out.

Plus, the less expensive tamoxifen is still more commonly prescribed in many other parts of the world, Gralow says.

The new findings also have implications for women taking aromatase inhibitors, she says.

"The study clearly shows that you need to take the majority of your pills to really get benefit. As we move toward greater use of aromatase inhibitors, which do not stay in the body as long, taking the drug as prescribed becomes even more important," Gralow tells WebMD.

Less Than Half of Women Took Tamoxifen for 5 Years

For the study, the researchers reviewed the records of 2,080 women treated for breast cancer between 1993 and 2002 in Scotland. Of the total, 79% were prescribed tamoxifen to reduce the risk of breast cancer returning after surgery.

Thompson notes that in Scotland, every patient has a unique 10-digit health number. This allowed the researchers to link data on each person's health status to pharmacy records.

Among the results:

• Although a 5-year course of tamoxifen is typically recommended, women took the drug for an average of 2.42 years.
• 37% of women stopped taking tamoxifen before 5 years, with 19% discontinuing its use 2 years into therapy.
• Less than half of women, 49%, took tamoxifen for 5 years.
• Women who didn't take tamoxifen at all had a 50% increased risk of dying, compared with women who took the drug.