Anastrozole, commonly known by its brand name Arimidex, is a medication primarily prescribed to postmenopausal women diagnosed with hormone receptor-positive breast cancer. This type of cancer relies on estrogen to grow, and anastrozole works to counteract this. While effective in treating breast cancer, patients often express concern about its recognized side effect of bone loss.
Understanding Anastrozole’s Impact on Bones
Anastrozole functions as an aromatase inhibitor, reducing estrogen levels in the body. In postmenopausal women, the ovaries no longer produce much estrogen; instead, it is primarily synthesized in other tissues, such as fat, through an enzyme called aromatase. Anastrozole blocks this enzyme, preventing the conversion of other hormones into estrogen.
Estrogen plays an important role in maintaining bone density and strength. When estrogen levels are reduced by anastrozole, the balance between bone formation and bone breakdown shifts. This shift leads to bone resorption, where old bone is broken down faster than new bone is formed. Over time, this imbalance decreases bone mineral density, leading to conditions like osteopenia (low bone density) and osteoporosis (fragile bones), and increasing fracture risk.
Timeline of Bone Density Changes
Bone density changes with anastrozole can begin quickly once treatment starts. Studies indicate bone loss can start within the first year of therapy. For instance, research from the ATAC (Arimidex, Tamoxifen Alone or in Combination) trial showed that women taking anastrozole experienced bone mineral density (BMD) decreases. After one year, there was a median decrease of 2.3% in lumbar spine BMD and 1.5% in total hip BMD.
This bone loss continues throughout treatment, though the rate may slow down over time in some areas. After five years of anastrozole use, women in the ATAC trial experienced a median decrease of 6.08% in lumbar spine BMD and 7.24% in total hip BMD. While the rate of loss in the lumbar spine appeared to decelerate between years two and five, the total hip BMD continued to decline at a consistent rate. Ongoing monitoring is important throughout treatment due to this sustained reduction in bone density.
Factors Affecting Bone Loss Risk
Several individual variables can influence the degree and speed of bone loss experienced while on anastrozole. A patient’s bone density before starting treatment is a significant predictor. Women who already have osteopenia or osteoporosis at baseline are at higher risk for further bone loss and developing full-blown osteoporosis. Conversely, those with normal bone density at the start of treatment are less likely to develop osteoporosis within five years.
Lifestyle choices also play a part in bone health. Factors such as insufficient dietary calcium and vitamin D intake, lack of weight-bearing exercise, smoking, and excessive alcohol consumption can all contribute to an increased risk of bone loss. Additionally, age, a history of previous fractures, and a family history of osteoporosis can elevate an individual’s susceptibility to bone density decline during anastrozole therapy.
Strategies for Bone Health During Treatment
Managing bone health while undergoing anastrozole treatment involves several proactive strategies. Regular bone density screenings, typically performed using DEXA (dual-energy X-ray absorptiometry) scans, are recommended. These scans help monitor changes in bone mineral density, allowing healthcare providers to detect bone loss early and intervene if needed. It is common practice to conduct a baseline DEXA scan before starting anastrozole and then follow up annually during treatment.
Incorporating lifestyle interventions can help mitigate bone loss. Adequate intake of calcium and vitamin D is important for maintaining bone strength. Healthcare providers often recommend daily supplements, such as 1000 mg of calcium and 400 IU of vitamin D. Engaging in regular weight-bearing exercise, like walking, jogging, or stair-climbing, also helps strengthen bones. For some patients, particularly those with pre-existing osteopenia or a higher risk of fracture, doctors may prescribe pharmaceutical interventions like bisphosphonates. These medications slow bone breakdown, helping preserve bone density.