Attention to bone health is an important aspect of managing breast cancer in women. Many women with breast cancer are postmenopausal and at increased risk for osteoporosis. Moreover, some of the agents used for the treatment of breast cancer have adverse effects on bones. For example, aromatase inhibitors (eg, anastrozole, letrozole, exemestane), which are used to treat early-stage breast cancer in postmenopausal women, deplete bone. Finally, bone is the most common site of metastasis in breast cancer. Metastasis to bone causes pain, pathological fractures, and spinal cord compression, as well as contributing to mortality.
What causes osteoporosis?
Our bones increase in density and strength until we reach our late 20s. Around the age of 35, we start to lose bone density as part of the natural ageing process. This happens gradually over time. A large reduction in bone density is known as osteoporosis. It is estimated that about half the population will have osteoporosis by the age of 75. The hormone estrogen protects against bone loss and helps to maintain bone density and strength. Women who have gone through the menopause are at increased risk of osteoporosis and fractures because their ovaries no longer produce estrogen.
Certain breast cancer treatments can speed up bone loss or cause you to lose more bone than you normally would:
In September 2011, denosumab (Prolia) was approved by the U.S. Food and Drug Administration (FDA) to increase bone mass in women at high risk for fracture who are receiving adjuvant aromatase inhibitor therapy for breast cancer. A dose of 60 mg is administered every 6 months. By inhibiting the development and activity of osteoclasts, denosumab increases bone density.
Vitamin D supplementation may be indicated in women treated for breast cancer, to aid with bone mineral density. Also, vitamin D supplements improved aromatase inhibitor–induced musculoskeletal symptoms in women on adjuvant anastrozole for breast cancer. Vitamin D also appeared to have a positive effect on bone loss on these patients.
Tamoxifen can be given to both pre-menopausal and post-menopausal women. It blocks the effect of estrogen, which helps stop breast cancer cells from growing. In pre-menopausal women, taking tamoxifen may cause a slight reduction in bone density. This is unlikely to lead to osteoporosis unless ovarian suppression is given as well. However, your risk may be higher if you’re 45 or under and your periods have stopped for at least a year.
Aromatase inhibitors are prescribed for postmenopausal women whose breast cancer has spread beyond the breast and lymph nodes. These drugs work by suppressing all estrogen production in the body. Studies using one of these drugs known as anastrozole, has shown a loss of bone density at the spine and hip. This effect seems to be more significant in women who are newly menopausal. There is also a very slightly increased risk of fracture for women taking this medication, although further research is needed in this area.
Different hormonal therapy and chemotherapy medicines can be used in your treatment plan, depending on the situation. And your treatment plan can change over time based on your needs, the benefits you're getting, and any side effects you may have. If you're worried about the effects of treatment on your bones, ask if you can change your treatment plan. During follow-up visits during treatment, ask your doctor about your bone health and whether protective measures are right for you.