Breast Cancer

Women undergoing treatment for breast cancer lose bone mineral density at a rate 2-3 times higher than disease free women.

Endocrine therapies such as aromatase inhibitors, surgical treatments (oophorectomy) and certain chemotherapy meds (anthracyclines, alkylating agents, and antimicrotubule agents) can lead to hypogonadism - one of the most common causes of secondary osteoporosis.

Estrogen identified as a key etiologic factor in the development of osteoporosis.  It acts on bone tissue via estrogen receptors on skeletal muscle.  Since estrogen inhibits osteoclasts, estrogen deficiency contributes to increased osteoclastic bone resorption with subsequent loss of bone mineral density and an increased risk of fracture.

Tamoxifen (selective estrogen receptor modulator or SERM) demonstrates both estrogenic and antiestrogenic effects.

• In postmenopausal women, tamoxifen acts as estrogen agonist on bone and serum lipids, resulting in lower cholesterol levels and bone density improvement.
• It is an estrogen antagonist in breast tissue of postmenopausal women which inhibits tumor growth.
• In premenopausal women, tamoxifen acts as an antagonist in both breast and bone tissue, resulting in tumor reduction as well as bone loss.

Aromatase inhibitors inhibit the conversion of androgens to estrone, the dominant circulating estrogen post menopause.  Induces hypogonadism.  In trial, a decrease in bone mineral density was observed at lumbar spine and hip of postmenopausal women treated with anastrazole.  Despite decreasing serum estrogen levels, there is no report change in calcium absorption with aromatase inhibitor therapy.

Calcium supplementation may potentially increase cardiovascular risk by increasing total cholesterol or by increasing oxidative stress.  Caution use in dyslipidemic postmenopausal women and limit use in premenopausal women.  Reminder that some breast cancer therapies already increase cardiovascular risk in survivors.

Goal:  meet RDA needs with diet sources and limit supplements to those who cannot meet needs with diet alone.  Encourage other bone health strategies such as weight bearing and resistance exercise.