5PSQ-121 Severe bone marrow aplasia induced by enfortumab vedotin in a patient with metastatic urothelial carcinoma: a case report and multidisciplinary management

<h3>Background and Importance</h3> Bone Marrow Aplasia (BMA) is a severe haematologic disorder characterised by bone marrow failure, leading to pancytopenia. This condition can result in life-threatening infections, bleeding, or severe anaemia. Causes include idiopathic factors, drug induced reactions, and viral infections. Enfortumab vedotin (EV) is an antibody-drug conjugate targeting nectin-4, used in metastatic urothelial carcinoma after failure of platinum-based chemotherapy or immunotherapy. Common side effects include peripheral neuropathy, dermatologic reactions, and moderate haematological toxicities. <h3>Aim and Objectives</h3> Describe the case of severe BMA in a patient following a single dose of EV. It also highlights the multidisciplinary management, emphasising the role of the hospital pharmacy team in treatment decisions and adverse event reporting. <h3>Material and Methods</h3> We performed a retrospective descriptive study on a patient treated with EV who developed BMA. Data were collected from the digital clinical history system. A literature review was conducted using the UpToDate-database. <h3>Results</h3> A 71-year-old male with metastatic urothelial carcinoma received multiple lines of treatment, including cisplatin+gemcitabine and atezolizumab. In March 2024, after further disease progression, our pharmacy team, together with the oncology department at the weekly tumour board, proposed EV based on the EV-301 trial, which demonstrated an overall survival improvement of 3.9 months over standard chemotherapy (hazard ratio 0.70; 95% CI: 0.55–0.85). Following approval by the hospital’s Pharmacy Commission, we administered 1.25mg/kg of EV. The patient initially presented mild symptoms (cough, fever), which were managed with antibiotics and dexamethasone. However, subsequent blood tests revealed severe pancytopenia (haemoglobin: 9.7g/dL, leukocytes:850 (400 neutrophils), platelets: 68.000). Haematology confirmed BMA via bone marrow biopsy. One month later, despite supportive treatment, the patient’s condition remained critical (haemoglobin: 9.6g/dL, leukocytes: 3.940, platelets: 66.000). Treatment with EV was discontinued, and we reported the adverse reaction to the national pharmacovigilance system. The Naranjo algorithm established a causality score of 5, confirming the link between EV and the adverse event. Options such as erdafitinib were considered but could not proceed due to the patient’s deterioration. He was referred to palliative care and passed away 2 months later. <h3>Conclusion and Relevance</h3> This case underscores the importance of active pharmacovigilance and multidisciplinary collaboration in identifying and managing severe toxicities like BMA following EV administration. Clinicians must remain vigilant for life-threatening haematologic events, ensuring rapid intervention to improve patient outcomes. <h3>References and/or Acknowledgements</h3> <h3>Conflict of Interest</h3> No conflict of interest