Adjuvant Endocrine Therapy and Bone Health in Breast Cancer

Breast cancer is one of the most common malignancies of women. The majority of breast cancers express estrogen and/or progesterone receptors, permitting anticancer targeting strategies to reduce estrogen signaling in the cancer cells and thereby lowering the risk of breast cancer recurrence. The development of the selective estrogen receptor modulator (SERM) tamoxifen marked a significant milestone in breast cancer care that transcended older estrogen ablative strategies such as oophorectomy and ovarian irradiation. An unintended benefit of tamoxifen in postmenopausal women was bone density preservation. The third generation of aromatase inhibitors (AIs) have demonstrated superior efficacy to tamoxifen in improving disease-free survival in postmenopausal women. However, the AIs significantly increase bone resorption, reduce bone mineral density, and increase the risk of fracture above that of tamoxifen. As a consequence of this, clinical oncologists have assumed a larger role in the screening and treatment of the skeletal complications of breast cancer therapies. The key features of managing bone health in women with early stage breast cancer receiving adjuvant endocrine therapy are reviewed here.

The UZ Leuven Policy for Extended Adjuvant Anti-estrogen Therapy in Women With Early Estrogen Receptor-Positive Breast Cancer

Opinion statement: Five years after adjuvant endocrine treatment for estrogen receptor (ER)-positive breast cancer, patients have a 2 to 20 % risk of metastatic relapse during the next 5 years. Extended adjuvant endocrine therapy seems to further lower this. In UZ Leuven, extended endocrine therapy is now discussed unless the tumor was a grade 1-2, pT1N0, ER-positive, progesterone receptor (PR)-positive, HER2-negative lesion. After 5 years of adjuvant tamoxifen treatment for ER-positive breast cancer, we encourage women to take another 5 years of tamoxifen. If the tumor was lymph node-positive at diagnosis and patients are menopausal after the first 5 years of tamoxifen, we advise to take prolonged treatment with an oral aromatase inhibitor (AI). For this particular group, available data for extending endocrine therapy with an AI after 5 years of tamoxifen are strongest and more convincing for letrozole than for anastrozole or exemestane. Under these conditions, letrozole is reimbursed for 3 years in Belgium. If women are postmenopausal at diagnosis and already used an oral AI at any time during the first 5 years, we discuss an extra 5 years of tamoxifen. Results from ongoing clinical trials will tell us whether in these cases prolonged AI use is better than tamoxifen so that therapy can be adapted. Benefit from extended adjuvant endocrine therapy is likely larger with better compliance and potential side effects of extended endocrine therapy need to be discussed. Therefore, when advising extended adjuvant endocrine treatment, a balance should always be made between relapse risk and treatment tolerance/compliance.