Medications Do More Than Prevent Breast Cancer

Breast cancer incidence lower in women taking selective estrogen receptor modulators

(RxWiki News) If you knew of a pill that was proven to reduce your breast cancer risks, would you take it? What if that same medication upped your chances of developing another type of cancer – would you still take it?

A new study that looked at some 83,000 women found that women taking selective estrogen receptor modulators (SERMs) were 38% less likely to develop breast cancer than those given placebo.

There was a downside, though. One of the medications significantly increased women’s risk of endometrial (lining of uterus) cancer.

And all SERMs increased the likelihood of deep vein thrombosis (blood clots in veins), mostly of the leg and thigh.

"Talk to your pharmacist about the risks and benefits of your prescriptions."

A group of researchers from around the world were led by Jack Cuzick, an epidemiologist at Queen Mary, University of London’s Wolfson Institute of Preventive Medicine.

About 70 percent of all breast cancers are estrogen receptor-positive, meaning that the hormone estrogen drives the growth of the cancer. SERMs interfere with this activity, blocking the estrogen that encourages the growth of breast cancers.

Researchers looked at nine prevention studies involving 83,399 women who were tracked for a median of about five and a half years. 

The scientists were evaluating the effectiveness of four medications: tamoxifen, raloxifene (marketed under the brand name Evista) and two medications that aren’t currently available in the US – arzoxifene and lasofoxifene.

The goal of the study was to measure how many women in the studies developed any form of breast cancer during a 10-year follow-up period.

Here are the combined findings:

  • Women taking a SERM were 38 percent less likely to develop breast cancer than women taking placebos (sugar pills).
  • Over a 10-year period, 6.3 percent of women taking placebo developed breast cancer compared to 4.2 percent of women taking a SERM.
  • The protective effects were seen for 10 years, with stronger influences in years 0 through 5.
  • Overall, invasive estrogen receptor positive (ER+) breast cancer was reduced from 4 percent to 2.1 percent.
  • Arzoxifene (not available in the US) reduced all breast cancer incidence by 58 percent and invasive ER+ breast cancer by 70 percent.
  • Those taking SERMs saw average 10 percent drop in LDL cholesterol.

Women taking tamoxifen had an increased incidence of endometrial cancer over those taking a placebo (103 cases versus 63 cases). This risk dropped when tamoxifen was stopped.

All SERMs increased the likelihood of deep vein thrombosis (375 cases versus 215).

“For all SERMs, incidence of invasive estrogen (ER)-positive breast cancer was reduced both during treatment and for at least 5 years after completion. Similar to other preventive interventions, careful consideration of risks and benefits is needed to identify women who are most likely to benefit from these drugs," the authors concluded.

According to Adam Brufsky, MD, PhD, professor of medicine at the University of Pittsburg School of Medicine, "Neither of these drugs [arzoxifene and lasofoxifene] are currently available, but this data is encouraging in that it is yet another example where intervention with a SERM or other anti-estrogen appears to prevent the development of breast cancer."

This study was published April 29 in The Lancet.

The research was funded by Cancer Research UK. Two of the authors were employees of Eli Lilly at the time of the study and one author has financial relationship with AstraZeneca.

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Review Date: 
April 29, 2013