RESUMO
BACKGROUND: There are no reliable and valid instruments in Mexico for breast cancer patients. Our objective was to measure reliability and validity of a Spanish version of the FACT-B (Functional Assessment of Cancer Therapy-Breast) questionnaire in Mexican population. METHODS: The translation of the questionnaire was reviewed and minor changes were made. The instrument was applied to 142 patients recently diagnosed with breast cancer. It was applied to 105 for the second time, and to 75 for the third time. An analysis of item discrimination was made. The questionnaire's reliability was determined by Cronbach's alpha. Concurrent validity was determined by an analysis of correlations between the instrument's scales and EORTC's QLQ C-30 y BR-23 scales. RESULTS: The five FACT-B subscales were reliable, their alpha coefficients varied between 0.65 and 0.82. The entire scale obtained a value of 0.87. The correlation analysis between FACT-B and EORTC QLQ C-30 subscales indicated that the same construct was being evaluated. CONCLUSIONS: FACT-B is a valid, reliable and sensitive instrument to measuring quality life in Mexican breast cancer patients.