Current and future status of adjuvant therapy for breast cancer

Adjuvant systemic treatments have greatly improved the prognosis of women with early breast cancer. Combination chemotherapy and, for patients with oestrogen receptor-positive (ER+) tumours, endocrine treatment has been found to reduce the frequency of relapse and improve survival. New adjuvant strategies include the introduction of taxanes into adjuvant chemotherapy schedules, the use of aromatase inhibitors in place of, or in addition to, tamoxifen, and the use of adjuvant bisphosphonates. Combination chemotherapy has been found to reduce the annual odds of recurrence and death in pre- and postmenopausal women. The benefits, however, are on average less in older patients. Anthracycline-based regimens are more effective than traditional regimens of cyclophosphamide, methotrexate, and fluorouracil (CMF). The benefits of adjuvant cytotoxic and endocrine treatments are additive. There is considerable debate as to the role of taxanes in adjuvant therapy. Improved outcome has been observed in one large trial, especially in those patients with ER-negative tumours. High-dose chemotherapy has not fulfilled its early promise. Ovarian suppression and/or tamoxifen remain the treatments of choice. The annual odds of relapse and death have been reduced by approximately one-third and one-quarter, respectively. Several very large studies are in progress to assess the potential of aromatase inhibitors in the adjuvant setting. Direct comparisons with tamoxifen, as well as switching after several years from tamoxifen to an aromatase inhibitor, are strategies under evaluation. Early results from one of these trials evaluating anastrozole (the Arimidex, Tamoxifen, Alone or in Combination [ATAC] trial) has reported a reduced relapse rate after a median follow-up of 3 years in favour of anastrozole. However, this was at the expense of accelerated bone loss, and strategies to minimise this side effect of aromatase inhibitors are under investigation. Although many studies have indicated that bisphosphonates prevent the development of metastatic bone disease in animals, the clinical role of prophylactic bisphosphonates in early breast cancer is not clearly defined. Three studies with oral clodronate have been published, two of them indicating a protective effect on the development of bone metastases and improved survival, and one suggesting a disadvantage to the use of adjuvant clodronate. Further large adjuvant trials with clodronate and zoledronic acid are in progress. Adjuvant bisphosphonates also have been found to reduce bone loss associated with cancer treatments and preserve skeletal health. It may be possible to replace the current oral regimens for prevention of bone loss with a single annual infusion of the highly potent bisphosphonate zoledronic acid.