Acute ST-Segment Elevation Myocardial Infarction Secondary to Neoplastic Infiltration of the Left Anterior Descending Artery

BACKGROUND: Neoplastic infiltration of the coronary arteries is an exceptionally rare cause of ST-segment elevation myocardial infarction and may closely mimic atherosclerotic acute coronary occlusion on clinical presentation and angiography. CASE SUMMARY: A 69-year-old woman presented with new-onset angina and worsening chest pain. Electrocardiography demonstrated ST-segment elevation in the anterior leads. Coronary angiography revealed long, smooth severe narrowing of the distal left anterior descending coronary artery, raising suspicion for type 2 spontaneous coronary artery dissection. Given hemodynamic stability and distal vessel involvement, a conservative strategy was pursued. Subsequent computed tomography angiography identified an anterior mediastinal mass infiltrating the anterior left ventricular wall, the left anterior descending coronary artery, 2 diagonal branches, and adjacent costal arches. Transthoracic biopsy confirmed squamous cell carcinoma of unknown primary origin. Care was redirected toward symptom-directed (palliative) management. DISCUSSION: This case highlights that anterior ST-segment elevation does not invariably reflect acute atherothrombotic coronary occlusion. Alternative mechanisms, including malignant coronary invasion, should be considered, particularly when angiographic findings are atypical. TAKE-HOME MESSAGES: Even in the presence of classic ST-segment elevation, nonatherosclerotic mechanisms must be considered. Multimodality imaging plays a critical role in identifying uncommon etiologies such as extrinsic compression or infiltrative malignancy.