The purpose of this exploratory, secondary analysis was to compare the prevalence of symptoms attributable to breast cancer or its treatment and to identify and describe symptom clusters across 3 phases of the disease. A pooled analysis was conducted by combining existing symptom data collected at the baseline assessment from 3 independent studies of women with breast cancer. Study I had 40 women with early-stage breast cancer following primary surgery for their disease and prior to the initiation of adjuvant therapy. Study II had 88 women with stage I, II, or III breast cancer who had completed surgery and adjuvant chemotherapy and may have been receiving hormonal therapy. Study III had 26 women with metastatic breast cancer (stage IV). Three symptom clusters were identified corresponding to 3 different phases of the breast cancer experience. Each cluster was composed of symptoms related to fatigue, perceived cognitive impairment, and mood problems. Future studies are needed to prospectively examine whether these symptoms cluster across 3 phases of breast cancer and the effect of these clusters on the functional ability and quality of life in women with breast cancer.