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Hormone Replacement Therapy: Type and Time Used Linked to Increase in Risk

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Very large studies have shown that using hormone replacement therapy (HRT) increases the risk of hormone-receptor-positive breast cancer. Results of a large study offer the same conclusions:

  • breast cancer risk goes up more with combination HRT (contains estrogen and progesterone) compared to estrogen-only HRT
  • the longer HRT is used, the more breast cancer risk increases

The California Teachers Study kept track of the health of nearly 57,000 retired women teachers over 10 years. The type of any HRT used and how long HRT was used were part of the health information recorded. During the 10 years, 2,857 women were diagnosed with invasive breast cancer. The researchers wanted to see if HRT use affected whether the women were diagnosed with breast cancer.

The results showed that women who used any type of HRT were 40% more likely to be diagnosed with invasive breast cancer compared to women who never used HRT. Also, women who used combination HRT had a higher risk of invasive breast compared to women who used estrogen-only HRT:

  • women who used combination HRT for 15 years or longer had an 83% increase in invasive breast cancer risk compared to women who didn't use HRT
  • women who used estrogen-only HRT for 15 years or longer had a 19% increase in invasive breast cancer risk compared to women who didn't use HRT

The longer a woman used HRT, the greater her risk of developing invasive breast cancer. Still, other research has suggested that most of the increase in breast cancer risk from HRT is linked to the first few years of HRT use.

The researchers also found that HRT use increased invasive breast cancer risk in normal weight and overweight women, but not in obese women (BMI of 30 or higher). This was true no matter which type of HRT the women used. The reason for this result isn't clear.

Other research on HRT and risk has shown that HRT use increases the risk of hormone-receptor-positive breast cancer but not the risk of hormone-receptor-negative breast cancer. This study also confirms that result. Most breast cancers are hormone-receptor-positive.

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. This and other studies strongly suggest that estrogen-only HRT increases breast cancer risk less than combination 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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