Abstract
Quality of life (QL) is used to assess treatments in clinical trials but may be influenced by other factors. We analysed the impact of biomedical, sociodemographic and cultural factors on baseline QL indicators in two International Breast Cancer Study Group trials. Patients with stage II breast cancer were randomized within 6 weeks of primary surgery to various adjuvant treatments. They were asked to assess five indicators of QL at baseline. QL forms were available for 1231 (83%) of the 1475 premenopausal and 989 (82%) of the 1212 post-menopausal patients, who were from nine countries and spoke seven languages. Culture (defined as language/country groups) had a statistically significant impact on baseline QL measures. Premenopausal patients with poor prognostic factors showed a tendency to report worse QL, with oestrogen receptor status as an independent predictor for mood (P = 0.0005). Older post-menopausal patients reported better emotional wellbeing (P = 0.002), mood (P = 0.002), and less effort to cope (P = 0.0009) compared with younger post-menopausal patients. Co-morbidity, type of surgery, treatment assignment and sociodemographic factors showed a statistically significant impact in post-menopausal patients only. Cultural and biomedical factors influenced baseline QL and should be considered when evaluating the impact of treatment on QL in international breast cancer clinical trials.