Tehran University of Medical Sciences Basic & Clinical Cancer Research 2228-6527 14 4 2023 10 29 220 232 Nneoma Okpalanma Chukwuemeka Odumegwu Ojukwu University, Igbariam Brian Ogbonna Faculty of Pharmaceutical Sciences, Nnamdi Azikiwe University, Awka Brian Ogbonna Faculty of Pharmaceutical Sciences, Nnamdi Azikiwe University, Awka 2022 12 03 2023 03 06 Background: Self-management process of diseases aims to equip patients with specific information that will improve compliance with prescribed medication and develop strategies that will help maintain quality of life.   Methods: A set of 35-potential self-management model was developed for the breast cancer patients in 2 domains from extensive literature search. The Instrument was validated using Delphi technique, item-total correlation analysis, factor analysis, construct validity and reliability analysis. Consensus was reached on the content validation of the self-management scale with mean score > 3.5, median > 3.5, absolute value between the median and mode < 1.00. Results: Forty-three items emerged after content validation in 2 domains: demographic characteristics of patients, and self-management content. Construct validity for selected items of the instrument showed values above 0.5. Item-total correlation analysis resulted in 31-items of the instrument. Factor analysis revealed a multi-dimensional instrument. The internal consistency of the instrument was determined with values between 0.5 - 0.8. Conclusion: Preliminary validation of the instrument showed the instrument to be valid but the internal consistency needs to be evaluated further with larger population size. The self-management scale revealed level of self-management among the breast cancer patients. This instrument should form a reliable tool for evaluating self-management in breast cancer patients in Nigeria.  https://bccr.tums.ac.ir/index.php/bccrj/article/view/458