New Research Underscores Link Between Hormone Replacement Therapy and Breast Cancer Risk

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Much research has shown a link between breast cancer risk and using hormone replacement therapy (HRT) to treat menopausal symptoms. The results from every study aren't exactly the same, but there's good evidence that:

  • HRT increases the risk of invasive breast cancer.
  • Breast cancer risk goes up in the first several years of HRT use; risk seems to keep increasing the longer a woman uses HRT.
  • Both combination HRT (contains both estrogen and progesterone) and estrogen-only HRT increase breast cancer risk, but combination HRT increases risk more.
  • High-dose HRT increases risk more than low-dose HRT.

A large study offers more support for these links between HRT and higher breast cancer risk. The results were presented at the 2012 Annual Meeting of the American Association for Cancer Research. Read the abstract of the study: Long-term use of hormone therapy and breast cancer incidence and mortality.

This study used information from the very large and ongoing Nurses' Health Study, which includes nearly 122,000 female nurses age 25 to 42 when they joined the study. Researchers have been tracking a number of the nurses' health factors for more than 20 years. In this case, researchers analyzed information on HRT use and breast cancer diagnoses among women who were postmenopausal between 1980 and 2008.

Echoing the results of earlier studies, this study found a much stronger link between combination HRT and breast cancer risk compared to estrogen-only HRT. It also found that breast cancer risk consistently increased the longer a woman used HRT.

Compared to women who never used HRT:

  • women currently using combination HRT for 10 to 15 years were 88% more likely to be diagnosed with breast cancer
  • women currently using combination HRT for 15 to 20 years were 150% more likely to be diagnosed with invasive breast cancer
  • women currently using estrogen-only HRT for 10 to 15 years were 22% more likely to be diagnosed with invasive breast cancer
  • women currently using estrogen-only HRT for 15 to 20 years were 43% more likely to be diagnosed with invasive breast cancer

Unlike women who were actively using HRT (called "current users" in the study), women who used HRT in the past, even for long periods of time, but stopped (called "past users") had only a slightly higher risk of breast cancer. This implies that breast cancer risk comes down after HRT stops. Other studies have found the same result.

Interestingly, the study found that while HRT use increased breast cancer risk, it didn't increase a woman's risk of dying from breast cancer.

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 an estrogen-only, low-dose formulation and try to take it for the shortest time possible. You also may want to ask about vaginal or transdermal HRT.

You can learn more about more about menopause and ways to manage side effects on the Managing Menopausal Symptoms pages.

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