Abstract Number: Esoc2026a961 Esus Beyond Atrial Fibrillation: The Importance of Oncological Investigation

Abstract Background and aims Approximately 30% of ischaemic cerebrovascular events remain of undetermined aetiology, including Embolic Stroke of Undetermined Source (ESUS). Beyond atrial fibrillation (AF), other potential mechanisms have been identified, such as artery-to-artery embolism, patent foramen ovale (PFO), and hypercoagulable states, particularly those associated with malignancy. It is estimated that 5–10% of ESUS cases are related to neoplastic disease. Methods Retrospective study of patients admitted with TIA or ischaemic stroke since 2021, classified as undetermined at discharge from the Stroke Unit, and followed for at least two years. Results Ninety-nine patients were included (47.5% women; mean age 73.1 ± 11.8 years). Five patients had active malignancy at the time of the index event, and eight were diagnosed during follow-up, totalling 13 cases (13.1%). A causal relationship was assumed in three patients, two of whom were anticoagulated. Two additional patients were subsequently diagnosed with AF and anticoagulated. In the remaining cases, no causal relationship was assumed due to localised disease or absence of recognised prothrombotic potential. During follow-up, AF was detected in 11 of 58 patients who underwent rhythm monitoring; PFO was identified in four of 22 investigated patients, and artery-to-artery embolism was presumed in three cases. Stroke recurrence occurred in three patients, one associated with active malignancy. Conclusions Despite the absence of systematic oncological screening, more than 10% of patients initially classified as having ESUS had a diagnosis of cancer at baseline or during follow-up. These findings highlight the relevance of considering malignancy in selected ESUS patients, given its implications for secondary prevention. Conflict of interest Jorge M. Ferreira Machado: nothing to disclose, Teresa Medeiros: nothing to disclose, Sofia Tavares: nothing to disclose, Diogo Fitas: nothing to disclose, Sandra Moreira: nothing to disclose, Cristina Duque: nothing to disclose, Maria João Lima: nothing to disclose