Adjuvant therapy for breast cancer

Significant progress has been made in the last 30 years in the adjuvant hormonal and chemo-therapeutic treatments of breast cancer. Currently, several cytotoxic agents are available for use including anthracyclines, taxanes, and cyclophosphamide, methotrexate and 5-fluorouracil (CMF) and a new class of hormonal agents, aromatase inhibitors were introduced. A greater than 50% improvement in risk of relapse and 25% absolute overall survival advantage is presently realistic for many women with lymph node-positive breast cancer who receive adjuvant therapy. Aromatase inhibitors (AI) now constitute a superior alternative to tamoxifen as adjuvant hormonal therapy in postmenopausal women with hormone receptor-positive breast cancer. Extended hormonal therapy with letrozole after completion of five-years of tamoxifen has been shown to improve survival and reduce late relapses. It has also been established that anthracycline containing combination chemotherapy is superior to CMF if the number of cycles is kept the same. Inclusion of a taxane in an anthracycline-based regimen has further improved efficacy. The schedule of administration of drugs, particularly of paclitaxel, also appears to have an impact on efficacy. On the other hand, increasing the dose of cyclophosphamide or anthracyclines above the standard dose do not appear to improve the efficacy of these regimens, whereas substandard dose are clearly inferior. Currently there are several highly effective adjuvant chemotherapy regimens, however there is no single best treatment, let alone a universally effective one. Tamoxifen was the first truly molecularly targeted agent to be used in the treatment of cancer though it took some time to understand that its benefits are restricted to hormone receptor-positive cancers only. Clinical experience shows that similar principals apply to adjuvant chemotherapy as well. Only a subset of patients with micro-metastatic disease benefit from cytotoxic therapy. A major current research effort is focused on the discovery of molecular markers that could predict who will benefit from what particular type of chemotherapy. In the near future, important clinical advances will come from the incorporation of trastuzumab into adjuvant chemotherapy regimens for patients with HER-2 amplified tumors. Results from several large randomized studies are expected shortly and will define the use of trastuzumab in this clinical setting.