Breast Cancer Prevention Drugs

New Information on Drugs Used to Prevent Breast Cancer

Postmenopausal women at a high risk of developing breast cancer may want to talk to their doctors about the drugs raloxifene (Evista) and tamoxifen (Nolvadex), according to new data from the STAR (Study of Tamoxifen and Raloxifene) trial.

One of the largest breast cancer prevention trials to date, STAR involved more than 500 cancer centers across the US, Canada, and Mexico. It began in 1999 and was extended in 2006 because initial results were unclear. These new results don’t settle the score on which drug is more effective, but suggest women discuss the pros and cons of each drug with their doctor in the context of their medical history and risk factors.

The STAR trial was funded by the National Cancer Institute (NCI) and led by researchers from the National Surgical Adjuvant Breast and Bowel Project (NSABP), a group that has conducted several large-scale clinical trials on breast cancer. The lead principal investigator was Victor G. Vogel, MD, MHS, formerly American Cancer Society National Vice President for Research.

In the study, almost 20,000 postmenopausal women were given either tamoxifen or raloxifene and were carefully followed to see whether they developed invasive or non-invasive breast cancer. Researchers also looked at whether side effects differed significantly between the 2 drugs. The follow-up period was extended for a median of 81 months, compared to 47 months in the initial trial.

Side effects of tamoxifen include fatigue, hot flashes, vaginal dryness or discharge, and mood swings. More serious side effects include an increased risk of developing cancers of the uterus and blood clots.

Raloxifene was initially used to help prevent osteoporosis (bone loss). It is also associated with an increased risk of blood clots.

Researchers found that the drugs were equally effective in reducing the risk of developing invasive breast cancer (50%), but women who took raloxifene had a slightly greater risk of developing invasive breast cancer than those who took tamoxifen (24% higher risk). Women on raloxifene also had a slightly higher risk of being diagnosed with this non-invasive disease

However, when it came to side effects, the women on raloxifene had 36% fewer uterine cancers and 29% fewer blood clots than the women who were assigned to take tamoxifen.

Death rates over the time of the study were the same for both groups of women, regardless of whether they took tamoxifen or raloxifene.

Based on these findings, the study authors conclude women at high risk for breast cancer discuss the pros and cons of each drug in context of their own medical history and risk factors. Women at high risk include those with a strong family history of the disease, certain genetic mutations (such as BRCA1 or BRCA2 mutations), or with a personal history of pre-cancerous breast changes. To learn more about each of these drugs, see Medicines to Reduce Breast Cancer Risk.

There are other ways to help lower your risk of developing breast cancer – keeping your weight in check, exercising regularly, and limiting your consumption of alcohol.