In this review of current pertinent literature from the fields of cancer epidemiology, oncology, health services research, and geriatrics, we describe the epidemiology and unique features of breast cancer and its victims in old age. In addition, we review the current evidence regarding treatment efficacy (i.e., beneficial under ideal circumstances) and effectiveness (i.e., beneficial under usual circumstances) in relation to primary tumor management and the use of adjuvant therapy in early stage disease and outline the challenges associated with studying breast cancer care in older women (> or = 65 years of age). Comorbidity, impaired functional status, lack of social support, and differences in host physiology are among the many factors that influence treatment efficacy and effectiveness, making extrapolation of study findings from younger to older women questionable. Indeed, with the exception of studies of adjuvant tamoxifen therapy, none of the clinical trials supporting the 1990 National Institutes of Health Consensus Development Conference on Treatment of Early-Stage Breast Cancer guidelines have included women over the age of 70 years. Because (a) breast cancer is becoming increasingly common in old age and (b) health-related quality of life is frequently more important to older women than is risk of recurrence or death, all three aspects (surgical management of the primary tumor, postoperative irradiation, and axillary lymph node dissection) of recommended primary treatment deserve fresh scrutiny. The value of adjuvant chemotherapy has yet to be defined. Substantial variations in breast cancer diagnosis, treatment, and care exist, and these differences become greater with increasing age of the patient. However, evidence regarding the reasons for these variations and their relationships with subsequent outcomes is lacking. Challenges for investigators in studies of older women include recruitment into studies, collection of reliable data from interviews or surveys, measurement of disease severity and comorbidity, and selection of relevant outcomes. Given current uncertainty about optimal treatment, clinicians can best serve older patients with early stage breast cancer by involving them in decision-making, taking into account available efficacy data, and individualizing care on the basis of such factors as comorbidity, social support, functional status, and patient preferences for outcomes. Future studies of treatment efficacy in older women should examine the roles of radiation therapy and axillary lymph node dissection that follow breast-conserving therapy and should focus on quality of life in addition to recurrence and mortality. Less aggressive treatments, tamoxifen therapy, and adjuvant chemotherapy should also be evaluated.