Back May 23, 2017

What’s Up With Bone Loss and Breast Cancer?

Did you know that some treatments for estrogen-receptor positive (ER+) breast cancer can cause bone loss? Recently, experts in the field compiled the data and made recommendations about how to handle this growing issue for the ~80% of patients diagnosed with this type of breast cancer.

Let’s start with a little background information. First the good news. As more and more women are being diagnosed earlier with ER+ breast cancer, most are living longer with the diagnosis and many patients are being treated for longer periods of time to help prevent the cancer from returning.

Estrogen and your bones

Now, the not so good news. Although quite effective for some women in preventing breast cancer from returning, some anti-estrogen treatments for post-menopausal women can lead to faster bone loss and higher risk of bone fractures. Why is estrogen important to bones? Bone is made of living tissue, and like all living tissue, it grows, breaks down, and forms again. This delicately balanced process is controlled in large part by hormones. However, if the bone “break-down” part of the natural process is happening at a greater rate than bone formation, bones lose density and the risk for bone fractures and osteoporosis increases. For women in menopause, the loss of estrogen is a main contributor to this process getting out of sync — naturally setting them up for higher rates of osteoporosis and possible fractures.1 Menopausal women who were treated with chemotherapy for estrogen receptor positive breast cancer are at additional risk for bone related issues.2 Anti-estrogen medications called aromatase inhibitors (AI) work by preventing non-ovarian estrogen production (estrogen sources in post-menopausal women come from the adrenal glands, fat, muscle and liver) by blocking the enzyme aromatase from converting androgen to estrogen.3 As described above, estrogen is necessary in the creation and keeping of strong bones. No estrogen can lead to weaker bones. This is called cancer treatment-induced bone loss (CTIBL).2

What’s the risk?

You may be asking yourself how serious this could be. Compared to the general population, breast cancer patients had a 25% increase in the risk of bone fractures and 18% increase in the risk of hospitalization due to bone fractures. The significant increase in risk of fracture persisted for 10 years.2 Women taking AIs were at a much greater risk of fracture compared to women taking tamoxifen (typically prescribed for pre-menopausal women with an ER+ breast cancer diagnosis). What’s more, and very concerning, was that breast cancer patients admitted to the hospital for bone fractures had 80% increased risk of death compared to those without fractures.2

Studies have demonstrated that one out of every 10 women taking an AI for 5 years will eventually have a bone fracture.  Importantly – experts point out that the rate of fracture of breast cancer patients outside of a clinical trial is likely to be may be as high as 18-20% when looking at real-world patient experiences.2 It has also been shown that after women stop taking AI treatment, bone mineral density may partially recover.2

Longer treatment, longer risk

Recently the bone health story has become more complicated as clinical trials show a benefit for some women who continue taking AI for up to 10 years. Studies showed that 3 to 5 of every 100 women will benefit from taking another 5 years of AI therapy for a total of 10 years. And about 100 women will need to be treated to prevent one metastatic recurrence of breast cancer.4 The timeframe around the fifth year of AI therapy may be a difficult one because more decisions about extending a woman’s treatment plan need to be made. The oncology treatment team and the patient will review multiple factors influencing the decision to extend AI therapy or to end treatment. All of the information regarding the patient’s stage and grade of breast cancer, lymph node involvement, and other laboratory and imaging tests performed since diagnosis, is assembled and reviewed. Surgical, radiation and chemotherapy treatments are also reviewed if applicable. A big factor in planning for future treatment is assessing how well a patient tolerated and took her treatment for the first 5 years. Did she experience severe side effects (for example, joint or muscle pain, hot flashes, vaginal dryness, loss of libido) or are there other health conditions that might be aggravated by continued therapy – like the bone loss issue discussed above?5 Has she taken the medication as prescribed by her doctor for the first 5 years? For women considering to continue with therapy beyond 5 years, an additional increased risk of fracture (2-3% increase each year) needs to be included in the assessment.2 There are other factors that increase the risk of bone fracture and include low body mass index (BMI), family history of hip fractures, rheumatoid arthritis, use of drugs like prednisolone for prolonged periods, and smoking.1,2

Weighing the benefit of extended treatment vs. potential risk

Many oncologists look beyond overall clinical trial results to the patient’s individual tumor biology for additional information to help with the decision-making. Today there are lab tests that “read” the original tumor to provide information about the risk of the cancer returning and the likelihood that the patient will benefit from 5 more years of anti-estrogen therapy. One such test that provides both important pieces of information is Breast Cancer IndexSM (BCI). BCI has helped thousands of doctors and tens of thousands of patients individualize decision-making for breast cancer treatment. BCI provides women who are lymph node negative or with up to 3 positive lymph nodes at diagnosis an individual risk percentage for the cancer returning after year 5 and a Low or High Likelihood of benefit from 5 more years of anti-estrogen therapy. Doctors then incorporate these test results with the other pieces of information into a recommendation for the patient.6

Ways to help keep your bones strong

For women and their physicians who decide that more treatment is indicated, these same experts have provided recommendations for use of supplements (like calcium and vitamin D) and other drugs determined to be safe and effective to help manage the side effect of bone loss due to on-going AI therapy.2 These drugs may be taken orally, or intravenously depending on your physician’s recommendation based on your individual situation. These drugs will be discussed in a future blog. Be sure to return to this page frequently for new information!


  2. Hadji, et al. Management of Aromatase Inhibitor-Associated Bone Loss (AIBL) in postmenopausal women with hormone sensitive breast cancer:Joint position statement of the IOF, CABS, ECTS, IEG,ESCEO, IMS, and SIOG, Journal of Bone Oncology 7 (2017) 1–12, Available online 23 March 2017
  4. Mamounas EP et al. San Antonio Breast Cancer Symposium, 2016.

For Breast Cancer Index Intended Use and Limitations visit