General
- Intracranial mesenchymal tumour with FET::CREB fusion is a provisional entity describing a mesenchymal neoplasm arising intracranially.
- It is characterised by variable histomorphology and a gene fusion involving a FET RNA-binding protein family gene and a member of the CREB transcription factor family.
Definition
- Essential criteria
- Diagnosis requires identifying a primary intracranial neoplasm with variable morphological features such as spindle cells, a mucin-rich stroma, or epithelioid cells in a mucin-poor collagenous stroma. AND
- Demonstration of a FET::CREB family fusion is an essential requirement for diagnosis.
- Desirable criteria
- Desirable features include the presence of CD99, EMA, and desmin immunoreactivity.
Numbers
- Most cases are identified in children or young adults.
- Occurrences have been reported in older adults into their sixties.
WHO grade
- This is currently a provisional entity and a specific CNS WHO grade is not assigned in the sources.
Histopathology
Microscopic
- The tumour cell morphology is diverse, ranging from monotonous round cells to stellate, spindle, or epithelioid and rhabdoid cells.
- Architectural patterns typically include reticular, cord-like, or sheet-like growth.
- A myxoid stroma is a common but inconsistent feature.
- Frequent findings include dilated, thin-walled vessels in an angiomatoid pattern and dense lymphoplasmacytic cuffing at the periphery.
Immunophenotype
- Expression of EMA, CD99, and desmin is common but can be variable.
- Tumours often show positivity for CD68 and CD163.
- Markers such as GFAP, OLIG2, SSTR2A, and cytokeratins are usually negative.
- Nuclear expression of SMARCB1 and SMARCA4 is typically preserved, which helps differentiate it from atypical teratoid/rhabdoid tumours.
- The Ki-67 proliferation index is generally low.
Pathogenesis
- These tumours are driven by a fusion between
- A FET RNA-binding protein family gene, usually EWSR1 and rarely FUS, ↔
- A member of the CREB family of transcription factors, such as CREB1, ATF1, or CREM.
- The specific cell of origin for these tumours remains unknown.
Localisation
- These intracranial masses are more frequently found in supratentorial than infratentorial sites.
- Most tumours are extra-axial and attached to the dura or meninges, though they may also be located within the ventricles.
Clinical features
- Patients present with symptoms related to mass effect and location, such as headache, nausea, vomiting, or focal neurological deficits.
- Seizures, tinnitus, anaemia, and haemorrhage have also been documented in some cases.
Radiological features
- On imaging, the tumours typically appear as circumscribed extra-axial masses attached to the meninges or dura, compressing the underlying brain.
- They often show lobulated growth with both solid and cystic components and avid contrast enhancement.
- Significant peritumoural oedema and intratumoural blood products are common findings.
Prognosis
- The full spectrum of clinical behaviour is not yet established, with outcomes ranging from slow growth to rapid recurrence.
- Rare instances of cerebrospinal fluid dissemination or systemic metastases to the bone, lungs, and lymph nodes have been reported.
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