Although the risk for distant recurrence of breast cancer is greatest in the first decade following definitive therapy, it persists for at least an additional decade. Systemic adjuvant therapy targets any remaining disease, reducing recurrence and improving long-term survival. The effects of various adjuvant therapies have been reported up to 10 years following diagnosis. In this overview, the Early Breast Cancer Trialists’ Collaborative Group reported 10- and 15-year results.
Authors of this overview sought information from 194 eligible randomized controlled trials that had started by 1995 and involved more than one month of systemic adjuvant therapy. Data were collected on each participant, including age, menopausal status, hormone receptor status, evidence of tumor spread, and type and duration of treatment. To adjust for the large number of variations among trials, event rate statistics were calculated for every trial and then added together to estimate the effects of treatment and describe differences among the outcomes of the various trials. The principal outcomes of interest were first recurrence of breast cancer, mortality (overall and from breast cancer), and incidence of other cancers.
Data were available on 4,000 women who received single-agent chemotherapy and on 29,000 women who received polychemotherapy. Both regimens reduced recurrence rates, but in general, there was a greater reduction in recurrence and mortality in women receiving polychemotherapy. The benefits were most marked in women who were younger than 50 years at diagnosis. Six months of therapy with an anthracycline-based combination (doxorubicin [Adriamycin] or epirubicin [Ellence] combined with f luorouracil and cyclophosphamide [Cytoxan]) was associated with an approximately 38 percent reduction in the annual mortality rate from breast cancer for women younger than 50 years. For women 50 to 69 years of age, the reduction was approximately 20 percent. Too few older women (i.e., 70 years and older) were enrolled in trials to estimate an effect. Additionally, regimens based on anthracycline were more effective than combinations of cyclophosphamide, methotrexate, and fluorouracil.
For women with estrogen-receptor–positive breast cancer, allocation to five or more years of treatment with tamoxifen (Nolvadex) reduced the annual mortality rate from breast cancer by an additional 31 percent. This effect appeared to be independent of age, tumor characteristics, or use of chemotherapy.
The authors conclude that the mortality rate over 15 years would be reduced by one half for the most common type of breast cancer patients (i.e., middle-age women with estrogen-receptor–positive tumors) by using a combination of anthracycline-based chemotherapy for six months followed by five years of tamoxifen.