Whether resilience should be conceptualised as a state or trait is debated. The precise distinction between state versus trait aspects of resilience can help identify dynamic targets for resilience-based intervention trials involving cancer patients. This study was designed to disentangle the state and trait components of resilience in patients with breast cancer with the help of Generalisability Theory (GT) methods. The relative contributions of state (temporary) and trait (enduring) aspects of resilience were calculated using a 10-item Resilience Scale Specific to Cancer (RS-SC-10) and GT methods. In all, 391 patients were enrolled from the 'Be Resilient to Breast Cancer ' (BRBC) trial, and data from 317 patients (81.7%) were collected at baseline, 3 months, 6 months, and 12 months after the intervention. The subscale of Generic Elements demonstrated high generalisability value (relative G-coefficient = 0.81) across different occasions and captured 79% of the variance attributed to enduring aspects of resilience. The subscale of Shift-Persist showed low generalisability value (relative G-coefficient = 0.31) and identified 59% of the variance attributed to temporary aspects of resilience. The GT studies suggested that 5-7 items per scale and three measurement occasions were adequate for score reliability evaluation. Resilience should be conceptualised as a state-trait mixed psychological variable in breast cancer patients. The subscale of Shift-Persist in RS-SC-10 is amenable to intervention and could be utilised as a primary outcome in resilience-based intervention trials. None. Copyright © 2020 Elsevier Ltd. All rights reserved.