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Hormone-Related Health Factors May Influence Breast Cancer Characteristics

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A study suggests that several hormone-related health factors may affect the risk of developing specific types of breast cancer.

The researchers compared the health histories of more than 1,000 women aged 55 to 79 who were diagnosed with breast cancer to the health histories of about 1,500 similar women who weren't diagnosed with breast cancer. The diagnosed breast cancers were of three different types:

  • 1,023 women were diagnosed with what the researchers call luminal breast cancer -- luminal breast cancer is commonly called hormone-receptor-positive breast cancer
  • 39 women were diagnosed with HER2-positive breast cancer
  • 78 women were diagnosed with what the researchers called basal-like or unclassified breast cancer -- this type of cancer is more commonly called triple-negative (HER2-negative, estrogen-receptor-negative, and progesterone-receptor-negative) breast cancer

The study found that:

  • Women who started having menstrual periods at an earlier-than-usual age were about 3 times as likely to develop HER2-positive breast cancer later in life compared to women whose periods started at the usual age. Starting menstrual periods early didn't influence the risk of developing hormone-receptor-positive or triple-negative breast cancer.
  • Women who breast fed their babies for at least 6 months were 20% less likely to develop hormone-receptor-positive breast cancer later in life than women who didn't breast feed. Women who breast fed also were about half as likely to develop triple-negative breast cancer.
  • Women who started to go through menopause at a later-than-usual age were 60% more likely to develop hormone-receptor-positive breast cancer compared to women who started to go through menopause at a more typical age.
  • Women who used combination hormone replacement therapy (HRT) were 70% more likely to develop hormone-receptor-positive breast cancer than women who didn't use HRT.

Hormone-receptor-positive breast cancer is more common and has a better prognosis than HER2-positive and triple-negative breast cancers. Hormones play an important role in the development and growth of hormone-receptor-positive breast cancers. Hormonal therapy medicines can effectively treat this type of breast cancer and can lower the risk of the breast cancer coming back.

The targeted therapies Herceptin (chemical name: trastuzumab) and Tykerb (chemical name: lapatinib) are used to treat HER2-positive breast cancers. Herceptin also can be used to lower the risk of HER2-positive breast cancer coming back.

Triple-negative breast cancer can be challenging to treat since hormonal therapies and targeted therapies aren't as effective in treating this type of breast cancer. Chemotherapy and radiation therapy can be used to treat triple-negative breast cancer.

Deciding to breast feed or to use HRT are personal choices that you can control. You can't control when you start having periods or when you start to go through menopause. A better understanding of any links between health factors -- whether or not they can be controlled -- and the development of different types of breast cancer can offer doctors more clues about how different types of breast cancer happen as well as how to treat each type.

This study found that the risk of hormone-receptor-positive breast cancer was 70% higher in women who used combination HRT compared to women who didn't use HRT. Other research has shown a similar link between HRT use and higher breast cancer risk. Still, the side effects of menopause, such as hot flashes, 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 taking HRT, talk to your doctor about:

  • How to keep your breast cancer risk as low as it can be. Other research shows that taking combination HRT for fewer than 3 years doesn't significantly increase breast cancer risk.
  • The pros and cons of different types of HRT. Estrogen-only HRT appears to increase breast cancer risk less than combination HRT.
  • A plan so you take HRT for the shortest time possible.

Together, you and your doctor can decide if HRT or another treatment to ease menopausal side effects might be right for you. If you decide to use HRT, try to make healthy lifestyle choices (eating a healthy diet, exercising) that can lower your breast cancer risk. During and after HRT, make sure to follow recommended breast cancer screening guidelines, including monthly breast self-exams, annual mammograms, and annual physical exams by your doctor.

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