Evaluating bone health in breast cancer patients

This review examines the role of bisphosphonates in postmenopausal (after menopause) women with breast cancer.

Menopause is the period in a woman’s life after menstruation stops and the ovaries become inactive, defined as 12 months after a woman's last period. With menopause, the level of female sex hormones such as estrogen also drops. This leads to progressive loss of bone mineral density or BMD (a measure for bone strength), causing the bones to become brittle and fragile, prone to fractures (breaks). This condition is called osteoporosis. The hormone estrogen helps maintain bone density, but also influences the growth of some breast cancers. Therefore, breast cancer patients often receive treatments that lower estrogen levels to stop the growth of breast cancer, also leading to a decrease in BMD and osteoporosis. In women with more advanced breast cancer, the cancer can spread (metastasize) to other areas of the body such as the bones, which also leads to a loss of BMD.

Bisphosphonates (BPs) such as zoledronic acid or zoledronate (Zometa, Aclasta), ibandronate (Bonviva), alendronate (Fosamax), risedronate (Actonel), clodronate (Bonefos) are a class of drugs called antiresorptives that slow or stop the natural process that dissolves bone tissue, thus maintaining or increasing BMD. BPs are commonly used to treat osteoporosis. Additionally, BPs create an environment in the bones that does not favor the survival of cancer cells.

A total of 27 studies evaluating the use of BPs in postmenopausal women with breast cancer were reviewed. These studies were grouped into two categories: studies that evaluated BMD preservation during breast cancer treatment and those that assessed the anticancer benefits of BPs.

Treatment with aromatase inhibitors or AIs (a type of hormonal treatment for breast cancer that lowers estrogen levels) such as anastrozole (Arimidex) often reduces BMD in breast cancer patients. Several studies have shown that risedronate 35 mg weekly improved BMD and reduced BMD loss in breast cancer patients treated with AIs. Also, ibandronate 150 mg every month improved BMD in the hip and lumbar spine in postmenopausal women treated with AIs. Other studies showed that alendronate 70 mg weekly reduced BMD loss after stopping tamoxifen (Nolvadex) treatment. Tamoxifen is a hormonal therapy drug that stops estrogen from getting to the breast, thus stopping the growth of breast cancer, but acts like estrogen in other tissues such as the bone, therefore preventing BMD loss. Zoledronate, 4 mg every 6 months given into the vein to postmenopausal women treated for breast cancer, improved BMD within 12 months, even in patients who had osteoporosis before the treatment.

In the assessment of BPs' anticancer effects, studies showed that clodronate lengthened the time without the cancer returning (recurrence-free survival) or spreading (metastasis-free survival) in older breast cancer patients. Also, zoledronate increased the time without any signs or symptoms of cancer (disease-free survival) by 25% in postmenopausal women treated for breast cancer compared to placebo (a substance with no medical effect used as a control when testing new drugs). 

In summary, the addition of BPs to breast cancer therapies in postmenopausal women helps prevent bone loss and promotes better outcomes in breast cancer patients.

While the benefits of BPs regarding bone health in patients treated for breast cancer are clear, further studies are needed in order to understand the anticancer effects of these drugs.