Women who do not fill most of their prescriptions for tamoxifen (Nolvadex) are at greater risk of death from breast cancer, a new study shows. Tamoxifen is a hormone therapy proven to reduce the return of breast cancer in women with cancers that are fueled by estrogen (called estrogen receptor-positive breast cancer). Doctors generally recommend that women take it for five years. However, some women experience menopausal symptoms, such as hot flashes, that are bothersome enough to cause them to stop taking this medication.

In this study, researchers reviewed the records of 2,080 women in Scotland treated for breast cancer between 1993 and 2002. Most women (79%) were prescribed tamoxifen after surgery. Pharmacy records were used to find out the proportion of tamoxifen prescriptions that had been filled. The women in the study took tamoxifen for an average of nearly two and one-half years (this time is lower than five years because when the study started there was no consensus about the best length of treatment). The researchers found that 10% of women picked up 70% or fewer of their tamoxifen prescriptions over the time that their doctors had prescribed the drug. These women had a 16% increase in the risk of death compared with women who picked up all of their tamoxifen prescriptions.

"While an occasional missed tablet is not a great worry, once you take tamoxifen less than 70% of the time, your survival significantly decreases," said Alastair Thompson, MD, Professor of Surgical Oncology at the University of Dundee, and the study's lead author.

What This Means for Patients

This study emphasizes the importance of taking all of the prescribed medication after surgery for breast cancer. Women are encouraged to talk with their doctors if they experience side effects from the medication that are disruptive enough to cause them to stop taking the medication. Often, these side effects can be treated, or the doctor can prescribe a different medication.