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Experimental Bone Medicine May Lower Risk

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A study shows that a new osteoporosis medicine, Oporia (chemical name: lasofoxifene), may reduce the risk of breast cancer, especially hormone-receptor-positive breast cancer. The results were presented at the 2008 San Antonio Breast Cancer Symposium.

Lasofoxifene is a SERM (selective estrogen receptor modulator), a type of hormonal therapy medicine. Because of the way they work in the body, SERMs can both 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 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. Half the women got lasofoxifene every day for 5 years. The other 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. The results showed lasofoxifene improved bone health and reduced breast cancer risk, compared to the placebo.

The findings from this study suggest that lasofoxifene may work better than either tamoxifen or Evista to reduce breast cancer risk in postmenopausal women being treated for osteoporosis. During 5 years of treatment, only 0.1% of the women who took lasofoxifene were diagnosed with breast cancer, compared to 0.8% of the women who took the placebo pill. This means that lasofoxifene reduced breast cancer risk by 85%. In comparison, other research has found that tamoxifen reduces breast cancer risk by 43% and that Evista reduces breast cancer risk by 72%, compared to placebo.

The U.S. Food and Drug Administration (FDA) is deciding whether lasofoxifene should be approved to treat osteoporosis and lower breast cancer risk in postmenopausal women.

If you're a postmenopausal woman and have osteoporosis or are taking steps to reduce your risk of developing osteoporosis, you and your doctor will probably consider a number of treatment options to improve your bone health. SERMs, such as Evista and lasofoxifene (which isn't available yet), 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.

Both SERMs and bisphosphonates may cause side effects.

The SERM Evista's side effects may include:

  • hot flashes
  • sweating
  • joint pain
  • leg cramps
  • flu-like symptoms
  • blood clots deep in the legs
  • a blood clot that travels to the lungs (called a pulmonary embolism)
  • stroke

A blood clot or stroke as a side effect of Evista may be serious and life-threatening.

Side effects of bisphosphonates may include:

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

Some of these side effects can be serious, but the risk of life-threatening side effects is lower with bisphosphonates than with Evista.

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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