Histopathological analysis of a retrieved cerebral thrombus revealed occult lung adenocarcinoma with high PD-L1 expression, demonstrating that tumour embolism is a rare but clinically relevant mechanism of ischaemic stroke that should be considered in embolic stroke of undetermined source.
Key Findings
Results
Histopathological examination of a mechanically retrieved cerebral thrombus revealed malignant epithelial cells consistent with lung adenocarcinoma.
The patient was a 76-year-old white European man presenting with acute left hemiplegia, hemianopsia, and dysarthria (NIHSS 18)
Immunohistochemical analysis confirmed the diagnosis of lung adenocarcinoma
High PD-L1 expression was identified on immunohistochemical staining
No prior cancer diagnosis had been established at the time of stroke presentation, making this an occult malignancy
Results
Subsequent chest CT identified a large necrotic lung mass invading the pulmonary vein, consistent with the tumour embolism mechanism of stroke.
The mass was located in the left lung
Pulmonary vein invasion provided the anatomical pathway for direct tumour embolism to the cerebral circulation
CT angiography had demonstrated occlusion of the right middle cerebral artery
Standard cardioembolic workup was negative, and D-dimer levels were only moderately elevated, suggesting tumour embolism can occur without classic laboratory or monitoring red flags.
Continuous cardiac monitoring and 72-hour Holter-ECG showed no atrial fibrillation
Transthoracic echocardiography identified no major cardioembolic source
Laboratory testing showed only moderately elevated D-dimer levels
Non-contrast CT showed early ischaemic changes with ASPECTS 7, and CT perfusion revealed a favourable mismatch profile
Results
Despite initiation of immunotherapy, the patient developed brain metastases and died 51 days after the index stroke.
Immunotherapy was initiated after the cancer diagnosis was established via thrombus histopathology
The patient developed brain metastases during the clinical course
Death occurred 51 days after the index stroke event
The rapid clinical deterioration underscores the aggressive nature of cancer-associated stroke via tumour embolism
Discussion
Tumour embolism should be considered as a mechanism in patients with embolic stroke of undetermined source, even in the absence of markedly elevated D-dimer levels.
Cancer-associated stroke is described as a heterogeneous entity in which hypercoagulability represents the most common mechanism
Direct tumour embolism is characterised as rare and likely under-recognised
The authors suggest histopathological analysis of thrombectomy specimens may provide clinically relevant diagnostic information
The case illustrates that routine thrombus analysis may facilitate early detection of occult malignancy in selected patients
What This Means
This case report describes a 76-year-old man who suffered a severe stroke caused by a blood vessel blockage in the brain. When doctors used a mechanical procedure to remove the clot, they sent it to a laboratory for analysis. Instead of finding a typical blood clot, pathologists discovered actual cancer cells inside it — specifically cells from a lung adenocarcinoma (a type of lung cancer) that had not previously been diagnosed. Further imaging revealed a large cancerous mass in the left lung that had grown into a pulmonary vein, allowing tumor fragments to travel directly to the brain and cause the stroke.
This research suggests that sometimes stroke can be caused not by a conventional blood clot but by fragments of a tumor breaking off and blocking blood vessels in the brain — a phenomenon called tumor embolism. Importantly, the usual warning signs that doctors look for to identify cancer-related clotting problems (such as very high D-dimer blood levels or abnormal heart rhythms) were absent or minimal in this patient, meaning the cancer would likely have gone undetected without the thrombus analysis. Despite starting immunotherapy after the cancer was identified, the patient developed brain metastases and died 51 days after the stroke.
This case highlights a potential diagnostic opportunity: routinely analyzing clots removed during stroke procedures (mechanical thrombectomy) might help detect hidden cancers in some patients. For patients who have a stroke with no clear cause found through standard testing, tumor embolism — though rare — should be considered as a possibility. Early identification of an underlying cancer, even at this late stage, could influence treatment decisions and provide important information for patients and their families.
Jauregui-Larrañaga C, Albajar I, Juaristi-Abaunz M, Marta-Enguita J. (2026). Histopathological analysis of a retrieved cerebral thrombus revealing occult lung adenocarcinoma: a case report.. Journal of medical case reports. https://doi.org/10.1186/s13256-026-06487-w