Purpose <p>The IMPACTOR study (IMPact of AbemaCiclib on patienTs’ rOles and Responsibilities–ISRCTN17281696) was developed to capture experiences of women with MBC being treated with abemaciclib in a real-world setting. The primary aim was to explore changes to quality of life over time and our secondary aim was to understand these changes in detail via qualitative interviews, as presented here.</p> Methods <p>A singular interview was offered to participants who had expressed an interest at the point of consent. These were all conducted remotely using a semi-structured interview topic guide.</p> Results <p>Twenty interviews were completed and analysed using a framework approach to thematic analysis. Eight themes were developed—COVID-19, experience of MBC, side effects, side effect management, treatment information and support, relationship impacts, impact on daily life, and finances and employment.</p> Conclusions <p>It was apparent that participants faced side effects from treatment but undertook steps to manage these as much as possible. Adaptations were often led by a belief about the benefits of remaining on treatment. Adjustments ranged from modifying routines to carrying personal hygiene supplies when out in public in case of diarrhoea. While this was anticipated, other side effects were less well known with variable clinical support and available information. Family support was raised frequently, predominantly in relation to the impact MBC had on roles and relationships. Themes from this work can be thought of via theories about treatment belief and adherence, such as the common-sense and self-regulation models, as participants reflected on both emotional and cognitive coping strategies.</p> <p>Trial registration - ISRCTN17281696.</p>