Psychometric validation of the Breast Cancer Treatment Outcome Scale (BCTOS-12): a prospective cohort study

The Breast Cancer Treatment Outcome Scale (BCTOS) is a questionnaire to evaluate the aesthetic and functional outcome after breast conserving surgery (BCS). The original BCTOS with its 22 items on three subscales was refined to a shorter, improved, and easier to administer patient-reported outcome measure, the BCTOS-12. The BCTOS-12 consists of 12 items on two distinct subscales, the Functional Status and the Aesthetic Status. The aim of this study was to validate the BCTOS-12 in a prospective cohort.

For this study, 239 breast cancer patients were included preoperatively, and 204 patients completed the BCTOS-12 and EORTC QLQ C30 BR23 shortly after their BCS, corresponding to a follow-up rate of 85%. The item-factor structure was examined by confirmatory factor analysis. The reliability was calculated by McDonald's Omega for estimating internal consistency. The convergent validity was assessed by Spearman's rank correlation coefficients between the related scales of the questionnaires.

The BCTOS-12 showed a robust item-factor structure and a good internal consistency with McDonald's Omega of 0.89 for the Aesthetic Status and 0.90 for the Functional Status. A high convergent and divergent validity was indicated by correlations between the subscales of the EORTC QLQ C30 BR23 and the BCTOS-12.

Overall, the results demonstrate a successful psychometric validation of the BCTOS-12. The BCTOS-12 is a refined, improved, and now validated, instrument. It can be used in clinical studies and routine management for the evaluation of the aesthetic and functional outcome after BCS.