Selective Estrogen Receptor Modulators Reduce Breast Cancer Rates by More Than a Third in Women at High Risk


Key Points

  • Researchers examined the effectiveness of four selective estrogen receptor modulators on breast cancer incidence in women at high risk for the disease.
  • A 42% reduction in breast cancer incidence was seen in the first 5 years in women who were taking a SERM compared with those who were not.
  • A 25% reduction in incidence was seen in the first 5 years of follow-up.

Tamoxifen and three similar drugs reduce breast cancer incidence by 38% in women at an increased risk of the disease according to a Cancer Research UK study published in The Lancet today.

In the most comprehensive study to date scientists calculate that one breast cancer would be prevented for every 42 women who took the drug for 5 years with 5 years follow-up.

Study Details

Researchers examined the records of more than 83,000 women to review the effectiveness of four selective estrogen receptor modulators (SERMs): tamoxifen, raloxifene (Evista), arzoxifene, and lasofoxifene. Tamoxifen is used to treat estrogen receptor (ER)–positive breast cancer, and the other agents are used to treat osteoporosis.

The first 5 years—when the women were taking the drug—showed the greatest decrease in incidence, with 376 breast cancer cases vs 594 for those who were not taking a SERM, a reduction of 42%.

A benefit was seen in the 5 years after the women had stopped taking the drug: 211 breast cancer cases in women who had taken a SERM compared with 258 in those who had not—a 25% drop. However, this reduction was not as great as that seen during the first 5 years. There was no effect on breast cancer deaths.

Side Effects

Researchers also examined the frequency of side effects of the drugs. All four drugs significantly increased the risk of blood clots such as deep vein thrombosis. Only tamoxifen showed an increase in endometrial cancers. The increase in cases fell after women stopped taking the drug.

The drugs also led to a reduction in the risk of fractures. The direct comparison of tamoxifen with raloxifene showed that raloxifene is less effective than tamoxifen, but has fewer side effects.

No effect was noted for ER-negative breast cancers but the reduction of ER-positive breast cancer was 51%.

‘Encouraging Results’

Jack Cuzick, PhD, lead researcher based at the Queen Mary University of London, said, “These are very encouraging results and pave the way for more widespread use of these drugs in high-risk women in a manner similar to the way statins and blood pressure–lowering drugs are used to reduce the risk of heart disease and stroke.”

Hazel Nunn, Cancer Research UK’s head of health information, added, “These results provide some of the clearest evidence to date of the ability of these drugs to prevent breast cancer. The study also offers clarity on the frequency of side effects that can be expected from these drugs. Breast cancer is the most common cancer in the UK, and research like this has the potential to reduce the number of women diagnosed with the disease in the future.”

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.