Case Report: An enlarging left ventricular mass during anticoagulation in a patient receiving almonertinib after thoracic radiotherapy: diagnostic uncertainty and individualized management.

Distinguishing a left ventricular thrombus from a cardiac tumor is challenging when a large mass arises at an atypical non-apical site, particularly in a patient with cancer. We describe a 37-year-old man with epidermal growth factor receptor-mutant non-small cell lung cancer receiving almonertinib who developed a broad-based posterior wall left ventricular mass while cancer imaging remained stable. At detection, the reported left ventricular ejection fraction estimate was 55%, and no regional wall motion abnormality was documented. Cardiac CT showed no calcification or appreciable arterial- or delayed-phase enhancement, and Doppler echocardiography showed no internal flow. Low-mechanical-index contrast-enhanced echocardiography showed no appreciable internal perfusion in the contemporaneous examination report; later archived images also showed persistent absence of perfusion, although early-phase cine loops were not retained for retrospective reassessment. These concordant avascular features supported the presence of a thrombus but were not diagnostic. Cardiac magnetic resonance was recommended but declined because of financial concerns, and histopathology was unavailable. After approximately 9 months of prescribed edoxaban 60 mg once daily with reported adherence, the maximum linear dimension increased from 39.7 to 51.0 mm. A posterior wall regional wall motion abnormality was first documented 5 months after mass detection and therefore could not explain the lesion already present at detection. Edoxaban levels and edoxaban-calibrated anti-factor Xa activity were not measured, and human interaction data for almonertinib and edoxaban were unavailable. This case highlights the need to keep the diagnosis qualified and to reassess alternative pathology and anticoagulant exposure when an imaging-supported left ventricular thrombus follows an unexpected course.