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Presentation type	E-poster
Title	Diagnosis and Management of Atypical Lipomatous Tumor of the Orbit: A Case Report

Purpose	To describe the clinical course, diagnostic challenges, and management of an orbital atypical lipomatous tumor (ALT) presenting as a rare subconjunctival mass with severe proptosis and mass effect, with molecular features overlapping with atypical spindle cell/pleomorphic lipomatous tumor (ASPLT), particularly due to RB1 loss.
Methods	Clinical, imaging, histopathological, immunohistochemical, and molecular findings were reviewed. After years of diagnostic uncertainty and multiple biopsies, globe-conserving debulking provided tissue for definitive histopathological and molecular diagnosis. Reconstruction included contralateral conjunctival autograft and amniotic membrane transplant.
Results	Initial biopsy suggested low-fat spindle cell lipoma. Analysis of the debulking specimen revealed an atypical spindle-cell lipomatous neoplasm with CD34 positivity, RB1 loss, and MDM2/CDK4 amplification. Although RB1 loss suggested ASPLT, MDM2/CDK4 amplification excluded ASPLT and established ALT. After globe-conserving surgery, the patient achieved excellent functional and cosmetic outcomes.
Conclusion	This case illustrates the diagnostic and therapeutic challenges of lipomatous orbital neoplasms with atypical extensive disease. Molecular genetic analysis established ALT, identifying the uncommon combination of RB1 loss and MDM2 amplification and resolving the diagnostic challenge of ASPLT. Despite extensive orbital disease, globe-preserving debulking and ocular surface reconstruction achieved excellent anatomical and functional outcomes. This case emphasizes integrated molecular diagnostics and individualized surgical strategies for rare orbital tumors.
Conflict of interest	No

Authors 1

Last name	RUYSSCHAERT
Initials	E
Department	Ophthalmology, Ghent University Hospital
City	Ghent

Authors 2

Last name	Roels
Initials	D
Department	Ophthalmology, Ghent University Hospital
City	Ghent

Authors 3

Last name	Ninclaus
Initials	V
Department	Ophthalmology, Ghent University Hospital
City	Ghent