Incidence and management of diarrhoea associated with abemaciclib and endocrine therapy for hormone-receptor positive, HER2-negative metastatic breast cancer: the UK patients' experiences.

Purpose: Addition of a CDK4/6 inhibitor to endocrine therapy (ET) prolongs survival in HR + /HER2-metastatic breast cancer (MBC). Gastrointestinal side effects, predominantly diarrhoea and abdominal pain, are common in patients receiving abemaciclib. This can potentially increase symptom burden, reduce quality of life (QoL) and affect treatment adherence. This longitudinal mixed-methods study with a 6-month follow-up explored patients' outcomes and experiences.

Methods: Participants (n = 44) completed validated QoL measures at study-entry and at 1, 3 and 6 months. Weekly diarrhoea diaries with free-text response options assessed bowel movements and self-management strategies. Optional interviews gathered insight in patients' experiences.

Results: Forty-two participants completed study measures at study-entry and 24 at 6 months. 17/42 reported no gastrointestinal side-effects. Above threshold diarrhoea (≥ 3 loose/liquid stools daily) was reported at least once by 25/42, with 3/42 having persistent symptoms. Strategies to control diarrhoea, employed by 28/42, included dietary modifications, non-prescribed medication-use and nonadherence (dose interruption or reduction). Meaningful decline on the QoL diarrhoea subscale was observed in 12/37 at 1 month, 13/28 at 3 months and 8/23 at 6 months. Free-text analysis showed that diarrhoea disrupted everyday life in those affected.

Conclusion: A proportion of this small sample of MBC patients treated with abemaciclib and ET-reported diarrhoea which affected symptom burden and QoL. Close symptom monitoring alongside targeted supportive/educational interventions should be introduced to reduce the negative impact on patients' lives.

Trial registration: ClinicalTrials.gov Identifier: ISRCTN17281696.