Experimental Osteoporosis Medicine May Reduce Breast Cancer Risk

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A study found that lasofoxifene (possible brand names are Oporia and Fablyn), an experimental osteoporosis medicine, reduced the risk of breast cancer, especially hormone-receptor-positive breast cancer, in postmenopausal women.

Lasofoxifene is a selective estrogen receptor modulator (SERM), a type of hormonal therapy medicine. Because of the way they work in the body, SERMs can improve bone health AND lower the risk of hormone-receptor-positive breast cancer. SERMs block the action of estrogen in breast cells and certain other cells by sitting in the cells' estrogen receptors. SERMs don't affect all estrogen receptors the same way because they're selective (as the name says). In bone cells, SERMs affect estrogen receptors the way estrogen does, so SERMs strengthen bones. In breast cells, SERMs block the receptors from interacting with estrogen, so breast cancer cells that rely on estrogen can't grow. Hormone-receptor-negative breast cancers don't have estrogen receptors, so aren't as likely to be affected by SERMs.

Tamoxifen and Evista (chemical name: raloxifene) are other SERMs that many women take to lower breast cancer risk. Both tamoxifen and Evista also improve bone health. Doctors prescribe tamoxifen to lower breast cancer risk in women at high risk and to lower the risk of hormone-receptor-positive breast cancer coming back. Doctors prescribe Evista to postmenopausal women with osteoporosis to improve bone health and lower breast cancer risk. Evista also is prescribed to lower breast cancer risk in postmenopausal women who don't have osteoporosis.

More than 8,500 postmenopausal women participated in the Postmenopausal Evaluation and Risk-reduction with Lasofoxifene (PEARL) study. The women were split into two groups:

  • half got either a low dose (0.25 mg) or a high dose (0.50 mg) of lasofoxifene every day for 5 years
  • half got a placebo (sugar pill)

All of the women also took vitamin D and calcium supplements, which can help maintain or improve bone health.

Both the high and low doses of lasofoxifene improved bone health compared to the placebo. The high dose of lasofoxifene also dramatically reduced breast cancer risk. The low dose of lasofoxifene did not.

Because most of the women in the study didn't develop breast cancer, the researchers compared the effects of lasofoxifene in 49 women who were diagnosed with breast cancer and 156 similar women who weren't diagnosed with breast cancer.

After 5 years of lasofoxifene treatment:

  • The risk of any breast cancer -- hormone-receptor-positive OR hormone-receptor-negative -- was 79% lower in women who got the 0.50 mg lasofoxifene dose compared to women who got the placebo.
  • The risk of hormone-receptor-positive breast cancer was 83% lower in women who got the 0.50 mg lasofoxifene dose compared to women who got the placebo.
  • The risk of back bone fractures was 42% lower and the risk of other bone fractures (hip for example) was 24% lower in women who got either dose of lasofoxifene compared to women who got the placebo.
  • The risk of heart attack or other coronary events was 32% lower and the risk of stroke was 36% lower in women who got either dose of lasofoxifene compared to women who got the placebo.

The Breast Cancer Risk Assessment Tool, also called a Gail score, was developed by the National Cancer Institute to help doctors and women determine breast cancer risk based on personal and family health factors. Women who have a Gail score higher than 1.66 (which means they're at high risk for breast cancer) are usually candidates for treatment with a SERM such as tamoxifen to reduce risk. Still, this study found that the high dose of lasofoxifene reduced breast cancer risk in women with a low Gail score, which means they would be considered at lower risk.

The high dose of lasofoxifene caused side effects common with other SERMS. The risk of blood clots, which can be dangerous, was higher. Women who took lasofoxifene also were more likely to have hot flashes, night sweats, and leg cramps compared to women who took the placebo. Lasofoxifene didn't seem to increase the risk of uterine cancer, a side effect of tamoxifen.

The U.S. Food and Drug Administration (FDA) is considering approving lasofoxifene to treat osteoporosis. Part of that consideration will be the added benefit of reducing breast cancer risk.

If you're a postmenopausal woman with osteoporosis or are taking steps to reduce your risk of developing osteoporosis, you and your doctor will probably consider a number of treatment options. Because lasofoxifene isn't approved by the FDA yet, you won't be able to choose that treatment. SERMs such as Evista and tamoxifen are one choice. Bisphosphonates are another group of medicines used to strengthen bones. Bisphosphonates include:

  • Actonel (chemical name: risedronate)
  • Boniva (chemical name: ibandronate)
  • Fosamax (chemical name: alendronate)
  • Reclast (chemical name: zoledronic acid)

Reclast is given intravenously once a year. The others are pills taken by mouth.

Bisphosphonates strengthen bones better than SERMs, but none of the bisphosphonates have been shown to lower the risk of breast cancer in women who've never been diagnosed.

Side effects of bisphosphonates may include:

  • upset stomach
  • muscle and joint pain
  • esophagus irritation
  • osteonecrosis of the jaw (in rare cases)

You and your doctor will need to weigh the risks and benefits of each treatment. You'll also need to consider your unique situation. Do you have a higher than average risk of breast cancer? If so, then Evista may be a good choice for you. Do you have a higher than average risk of breaking a bone? If so, you may opt for the added bone-strengthening ability of a bisphosphonate. Together, you and your doctor can decide what makes the best sense for YOU. Whatever your choice, also ask your doctor about whether vitamin D and calcium supplements should be a part of your overall plan to improve your bone health.

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