RESUMEN
The aim of this study was to validate the Mexican-Spanish version of The European Organization for Research and Treatment of Cancer (EORTC) QLQ-BR23 questionnaire. The translation procedure followed EORTC guidelines. QLQ-C30 and QLQ-BR23 instruments were completed by Mexican women with breast cancer, attending a teaching referral cancer centre from February 2009 to January 2010. Patients were divided in two groups: (1) Patients with early stage of breast cancer; and (2) Patients with locally advanced breast cancer (LABC). Reliability and validity tests were performed, and validity over time (responsiveness) was conducted in a subset of patients. Two hundred and thirty-four women (mean age, 52.3 years) completed both questionnaires. Convergent and divergent validity was adequate. Cronbach's alpha of all multi-item scales showed values ≥0.7 except for Cognitive and Breast symptoms scales (0.52 and 0.65 respectively). Patients with early stages (n= 77) showed better functional scores and lower symptoms scores than patients with LABC (n= 157). Score means variation after responsiveness analysis demonstrated high sensitivity to change after breast cancer surgery. The Mexican-Spanish version of the EORTC QLQ-BR23 questionnaire is a valid and suitable instrument to estimate HRQL in patients with breast cancer.