Symptom measurement in the Breast Cancer Prevention Trial (BCPT) (P-1): Psychometric properties of a new measure of symptoms for midlife women

Purpose: To evaluate scalability of a symptom scale administered to women enrolled in the Breast Cancer Prevention Trial (BCPT) (P-1) conducted by the National Surgical Adjuvant Breast and Bowel Project (NSABP). Patients and methods: Responses of 11,064 women recruited into a study of 20 mg daily tamoxifen versus placebo to prevent breast cancer in high-risk women were analyzed. Exploratory factor analyses of the 12 month data were conducted on a random subset of 4,000 women to estimate the factor structure. Baseline data on these same 4,000 women were analyzed to confirm the structure. The remaining sample was divided randomly into two data sets. Data on each set were then grouped by age (35-49, 50-59, or ≥60 years) and treatment (tamoxifen or placebo) to corroborate these analyses. Correlations between the obtained symptom clusters and two standard instruments (SF-36 and CES-D) were examined. Content analysis of open-ended responses was also conducted. Results: Eight clinically-interpretable clusters of symptoms were identified and confirmed: Cognitive symptoms, musculoskeletal pain, vasomotor symptoms, nausea, sexual problems, bladder problems, body image, and vaginal symptoms. Scoring for each scale represented by these eight clusters is provided. Content analysis of open-ended responses suggested four items that are additional candidates: fatigue, back problems, abdominal pain, and leg/foot cramps or pain. Conclusions: Symptoms associated with hormone therapy for breast cancer can vary. Nevertheless, the BCPT Eight Symptom Scale (BESS) can be clustered into clinically relevant and reproducible factors that may be useful in future outcomes research.