Supplementary Material for: Epiploic Appendagitis in a Breast Cancer Patient on Abemaciclib: Case Report

Introduction: Epiploic appendagitis is an uncommon cause of acute abdominal pain, often mimicking surgical emergencies. This case highlights the diagnostic process for epiploic appendagitis in a breast cancer patient receiving abemaciclib, a CDK4/6 (Cyclin-dependent Kinase) inhibitor, and discusses potential associations with targeted therapies. Case Presentation: We present a case of a 48-year-old female on adjuvant abemaciclib for Stage IIIA breast cancer who developed acute left iliac fossa (LIF) pain. Clinical assessment, laboratory investigations, transvaginal ultrasound, and subsequent computed tomography (CT) imaging of the abdomen and pelvis were performed to establish the diagnosis. CT imaging revealed a characteristic oval fat-density lesion with surrounding inflammation adjacent to the sigmoid colon, consistent with epiploic appendagitis. Other differential diagnoses, including ovarian pathology and diverticulitis, were excluded. The patient was managed conservatively with analgesia, and the abemaciclib was temporarily discontinued and restarted at a lower dose, leading to symptom resolution. This case underscores the importance of considering epiploic appendagitis in the differential diagnosis of acute abdominal pain, particularly in patients on targeted therapies like abemaciclib, which are known to have gastrointestinal side effects. Timely and accurate diagnosis via imaging avoided unnecessary surgical intervention. Conclusion: This case is the first of its kind to propose a novel association between the use of targeted therapies such as abemaciclib and the development of inflammatory conditions such as epiploic appendagitis. It emphasises the crucial role of clinical suspicion and appropriate imaging in establishing this rare diagnosis. Further research is warranted to explore potential links between CDK4/6 inhibitors and the development of epiploic appendagitis.