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Patient Resources

Breast Cancer and Bone Loss

January 23, 2022

Breast cancer is one of the most common cancers in U.S. women (1 in 8 women). However, men also can get breast cancer.  

Hormonal therapy for breast cancer can lead to high rates of fractureup to 10-20% after five years of use, especially in post-menopausal women. Broken bones can lead to pain and disability. For example, many older people who break a hip lose their ability to function independently.

Connection to the Endocrine System 

Certain treatments for breast cancer can lead to bone loss because they decrease estrogen, the main female hormone. Estrogen triggers a woman’s sexual development, including the growth of breasts and regulation of her menstrual cycle. 

At menopause, usually around age 51, the ovaries stop producing estrogen, but small amounts are still made from pre-hormones (substances that are converted to hormones) produced by the adrenal glands (small glands on top of your kidneys). These pre-hormones are then changed into estrogen by fat tissue. 

Estradiol is one of three estrogen hormones naturally produced in the body. The effects of estradiol are clearly seen in women experiencing menopause. During this process, women naturally have lower levels of estradiol as the ovaries no longer produce it, causing the menstrual cycles to stop. This change often causes mood swings, vaginal dryness, hot flashes, and night sweats — the symptoms commonly associated with menopause. Over time, lower estradiol levels can lead to osteoporosis

In addition to its role in female development and reproduction, estrogen increases bone density (size and strength), prevents bone loss, and lowers the risk of fractures. Estrogen also travels through the bloodstream and attaches to certain cells in your body.  

This is a problem because breast tissue has these types of cells and is one of the main targets for estrogen. Estrogen stimulates the growth of breast cells. For this reason, if a woman develops cancer cells in her breast, estrogen can promote the growth of that cancer. However, with less estrogen, your bones are more likely to become weak and break easily. 

An X-ray scan (bone mineral density test) checks the strength of bones by assessing bone mineral density. The test can show early bone loss before the more serious condition of osteoporosis develops. Doctors recommend the following steps to prevent bone loss and avoid fractures. 

Take medicines as needed: Osteoporosis can’t be cured. But some medicines can prevent or treat osteoporosis. One class of medications, called bisphosphonates, can be taken as a pill every week or month or can be given intravenously (through a vein) in a doctor’s office or hospital once a year. These medicines keep bones strong by preventing bone breakdown and helping them retain calcium. New studies also suggest that these medications may help prevent cancer spread (metastases) in women with a high risk of recurrence, especially in post-menopausal women.  

Get enough calcium and vitamin D: You should get 1,000 to 1,200 mg of calcium and 1,000 to 2,000 IU of vitamin D each day. Good sources of calcium include milk, yogurt, cheese, collard greens, and foods with added calcium. Vitamin D, which helps the body absorb calcium, is made in the skin when people spend time in the sun. It’s also found in salmon, shrimp, and milk with added vitamin D. In addition to choosing foods with calcium and vitamin D, many people need dietary supplements to get enough of these nutrients. 

Exercise regularly: Weight-bearing exercise, such as walking, running, dancing, and climbing stairs, helps keep bones strong. So do exercises that strengthen muscles. 

Take other steps to live a healthy lifestyle: Maintain a healthy weight, avoid smoking and limit alcohol to no more than one drink a day.  

The choice of treatments for bone loss is based on whether a patient is at risk of fractures. Aside from cancer treatment, other factors that increase risk of bone loss include:

  • Personal or family history of bone fractures after age 65 
  • Being thin 
  • Smoking 
  • Having four or more alcoholic drinks a day
  • Certain diseases such as rheumatoid arthritis
  • Taking corticosteroids for more than 6 months
  • Low bone mineral density.

The choice of treatment is based on the type of breast cancer and other factors. Treatments that can decrease estrogen include: 

  • Surgery: Surgery is used to remove cancerous tissue in the breast or in other parts of the body. Sometimes one or both ovaries are removed to eliminate the main source of estrogen.
  • Radiation and Chemotherapy Drugs: These drugs can destroy cancer cells or stop their growth. They can also damage the ovaries and cause early menopause.
  • Hormonal Therapy: This stops the growth of Estrogen Receptor (ER)-positive breast cancer cells by stopping the production of hormones or blocking their action. Medicines used for hormonal therapy include:
  • Estrogen Receptor Antagonists
  • Aromatase Inhibitors (AI)
  • Luteinizing Hormone-releasing Hormone (LHRH) Analogs
  • Selective Estrogen Receptor Modulators (SERMs)
  •  

    These anti-estrogen therapies can cause bone loss. Your doctor will need to monitor for this and potentially give you treatment to reduce the risk of fractures.  

    Aromatase Inhibitors (AI)  

    Aromatase Inhibitors (AI), such as anastrozole, exemestane, and letrozole, prevent estradiol from being made. However, for postmenopausal women, Al therapy is very useful for treating ER-positive breast cancer but can be especially damaging to bones. 

    Estrogen Receptor Antagonists 

    Estrogen receptor antagonists, such as fulvestrant, block estradiol action. Estradiol is one of three estrogen hormones naturally produced in the body. If the body does not have enough estradiol, bone growth and development are slowed, and adults can develop osteoporosis.

    Luteinizing Hormone-releasing Hormone (LHRH) Analogs 

    Luteinizing Hormone-releasing Hormone (LHRH) analogs, such as goserelin and leuprolide, induce medical menopause. Medical menopause, like natural menopause, lowers the amount of estrogen in the body, thereby increasing the risk of bone loss and osteoporosis.

    Selective Estrogen Receptor Modules (SERMs) 

    If you are at high risk of developing breast cancer, your doctor may recommend a class of drugs called selective estrogen receptor modulators, which blocks the effect of female hormones, The U.S. Food and Drug Administration (FDA) has approved two SERMs to prevent breast cancer: 

    Tamoxifen: This drug is used for breast cancer prevention in pre- and postmenopausal women (aged 35 and older) who are at high risk. Tamoxifen prevents estrogen from stimulating the growth of breast cells that could become cancerous. 

    Raloxifene: This drug is FDA approved for breast cancer prevention as well as for preventing and treating osteoporosis (brittle bones) in postmenopausal women. Ralxifene works nearly as well as tamoxifen in reducing breast cancer risk in postmenopausal women. 

    Tamoxifen and raloxifene only reduce the risk of breast cancer by 50%. The decision to take these medications always depends on the balance between the benefits and risks. Side effects can include uterine cancer (with tamoxifen only), stroke, and blood clots in the veins and lungs. Your doctor will work with you to find the best option for you. 

    • What is my risk for breast cancer?
    • If I'm at high risk, should I take medication to prevent breast cancer?
    • How often should I do breast self-exams?
    • How often do I need to get a mammogram?
    • What is my risk for osteoporosis?
    • Would bisphosphonate medicines or denosumab help me?
    • What else can I do to prevent bone loss?
    • Should I see an endocrinologist for my condition?

    Image of hormones and breast cancer infographic.

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