INTRODUCTION Although modern technology has extended the survival of breast cancer patients, treatment’s adverse effects impact their health-related quality of life. Currently, no instrument exists capable of identifying the range of problems affecting breast cancer patients receiving radiotherapy in Cuba’s socioeconomic and cultural context.

OBJECTIVES Construct and validate an instrument to measure the effects of breast cancer and radiotherapy on health-related quality of life in Cuban patients.

METHODS The study was conducted at the Oncology and Radiobiology Institute, Havana, Cuba, from January 2010 through December 2011. Inclusion criteria were: adult female, histological diagnosis of breast cancer, treated with ambulatory radiotherapy, and written informed consent; patients unable to communicate orally or in writing, or who had neurologic or psychiatric conditions were excluded. Development phase: focus groups guided by a list of questions were carried out with 50 women. The patients reported 61 problems affecting their health-related quality-of-life. A nominal group (six oncologists and two nurses) identified the same problems. A syntactic analysis of the information was performed to create items for study and measurement scales. Content validity was determined by a nominal group of seven experts using professional judgment. Another 20 patients were selected to evaluate face validity. Validation phase: the instrument was applied to 230 patients at three different points: before radiotherapy, at the end of radiotherapy and four weeks after radiotherapy was concluded. Reliability, construct validity, discriminant validity, predictive validity, interpretability and response burden were evaluated.

RESULTS The final instrument developed had 33 items distributed in 4 domains: physical functioning, psychological functioning, social and family relationships, and physical and emotional adverse effects of disease and treatment. There were two discrete items: perceived general health and perceived health-related quality of life. Content validity and face validity were assessed as acceptable, by experts and patients respectively. Homogeneity, construct validity, and discriminant validity were satisfactory. The best results were obtained with test–retest reliability, predictive validity, and interpretability; the low rate of unanswered questions indicated that the instrument did not produce excessive patient response burden.

CONCLUSION The new instrument fulfilled the requirements for measuring impact of breast cancer and of radiotherapy on health-related quality of life in these Cuban patients, validating its usefulness for inclusion in clinical trial protocols.

KEYWORDS Psychometrics, quality of life, breast cancer, radiotherapy, Cuba