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Study Reinforces Link Between Breast Cancer Risk and Hormone Replacement Therapy

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A number of studies have shown a link between breast cancer risk and using hormone replacement therapy (HRT) to treat bothersome menopausal symptoms. While all the results don't perfectly agree, there is good evidence that:

  • HRT increases the risk of being diagnosed with invasive breast cancer.
  • HRT increases the risk of recurrence (the breast cancer coming back) in women who've been diagnosed.
  • Risk increases within the first several years of HRT use; risk appears to be greater the longer a woman uses HRT.
  • Combination HRT (contains both estrogen and progesterone) increases breast cancer risk more than estrogen-only HRT.
  • High-dose HRT increases risk more than low-dose HRT.

A study found that women who used combination HRT were nearly twice as likely to die from breast cancer compared to women who never used HRT.

The results are from a new analysis of information from the very large Women's Health Initiative (WHI) study. Some of the strongest evidence on the link between breast cancer risk and HRT comes from the WHI. When WHI results on HRT and breast cancer risk were released in 2002, doctors and public health officials recommended that if HRT is used, it should be used with caution. The results caused a major drop in HRT use in the United States, which was followed by a drop in invasive breast cancer diagnoses.

When the WHI study started in 1993, about half of the more than 16,000 postmenopausal women in the study got combination HRT. The other half got a placebo. After more than 5.5 years, an early analysis showed that the women on HRT were much more likely to be diagnosed with breast cancer compared to the women who got the placebo. So in 2002, ALL the women in the study stopped taking the medications, both HRT and placebo. Another analysis several years after the medicines were stopped showed that breast cancer risk in women who got HRT decreased some, but that risk was still higher that the risk in women who didn't take HRT.

When the main WHI study ended, more than 12,700 of the women in the study agreed to be part of a study extension. By 2005, after about 11 years of follow-up since the WHI started, results showed that compared to women who didn't get HRT, women who did get HRT:

  • were still 25% more likely to be diagnosed with breast cancer
  • were nearly twice as likely to have died from breast cancer: 25 women who got HRT died from breast cancer compared to only 12 women who didn't take HRT

Menopausal side effects can dramatically reduce quality of life for some women. These women have to weigh the benefits of HRT against the risks. If you're having severe hot flashes or other menopausal side effects and are considering HRT, talk to your doctor about all of your options. Ask how you can minimize your breast cancer risk AND relieve your symptoms. Be sure to discuss the pros and cons of different types of HRT. If you do decide to take HRT, ask if you can take a lower-dose formula and try to take it for the shortest time possible.

Learn more about more about menopause and ways to manage side effects in the Managing Menopausal Symptoms pages.

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