Surgical Pathology Criteria

Atypical Lipomatous Tumor

Differential Diagnosis

 

Lipoma vs Atypical Lipomatous Tumor (Well Differentiated Liposarcoma)

Pleomorphic Lipoma vs Atypical Lipomatous Tumor

Hibernoma with predominant mature fat Atypical Lipomatous Tumor
Small, central bland nuclei in vacuolated cells Lipoblasts, if present, have atypical nuclei
Lacks atypical nuclei Contains atypical nuclei
Frequently superifcial Rarely superficial
MDM2, CDK4, p16 negative MDM2, CDK4, p16 most positive

Myxoid Liposarcoma Atypical Lipomatous Tumor
No large atypical nuclei Large atypical nuclei present
Prominent "chicken wire" vascular pattern Lacks "chicken wire" vascular pattern
Rare as a primary lesion in retroperitoneum Frequently occurs in retroperitoneum
MDM2 and CDK4 4% by immunohistology but 1/5 MDM2 by FISH MDM2 and CDK4 most positive

Pleomorphic Liposarcoma Atypical Lipomatous Tumor
Lacks mature fat Prominent mature fat
Highly cellular Low cellularity
Mitotic figures frequent Mitotic figures rare
MDM2 and CDK4 negative MDM2 and CDK4 most positive

Fat Necrosis Atypical Lipomatous Tumor
Small central nuclei Large eccentric nuclei
Nuclei not indented by vacuoles Vacuoles indent nuclei in lipoblasts
Foamy cells frequently fill spaces of dead lipocytes Lipoblasts scattered

Angiomyolipoma Atypical Lipomatous Tumor
Large atypical blood vessels No large vascular component
Large epithelioid cells No large epithelioid cells
HMB45 positive HMB4 negative
MDM2 and CDK4 negative MDM2 and CDK4 most positive

Subconjunctival herniated fat and fat adjacent to renal cell carcinomas have been reported to simulate atypical lipomatous tumor

Spindle Cell Lipoma Spindle Cell Variant Atypical Lipomatous Tumor
Restricted to back of neck, upper back, shoulders Various locations
Bland spindle cells Mild to moderate atypia of spindle cells
Ropy collagen bundles No ropy collagen
Circumscribed May be infiltrative
Uniformly strong CD34 CD34 only occasionally reactive
MDM2 0-12% and CDK4 0-6% MDM2 and CDK4 most positive
No areas of usual ALT pattern Areas of usual ALT pattern
MDM2 and CDK4 figures given for usual ALT as no data for spindle cell variant

Neurofibroma Spindle Cell Variant Atypical Lipomatous Tumor
Hypocellular Moderated cullularity
No mitotic figures Occasional mitotic figures
No nuclear pleomorphism Mild to moderate atypia
S100 positive Spindle cells S100 negative

Dermatofibrosarcoma Protuberans Spindle Cell Variant Atypical Lipomatous Tumor
No cytologic atypia Mild to moderate atypia
Entrapped fat at periphery Fat integral to lesion
No lipoblasts Lipoblasts frequently present
CD34 may be extensive CD34 only in scattered cells

Spindle Cell Atypical Lipomatous Tumor Low Grade Fibromyxoid Sarcoma
Adult fat integral to lesion No fat component
Lipoblasts may be present No lipoblasts
Abnormal mitotic fibures may be present No abnormal mitotic figures
Areas may be histologically identical

Low Grade Myxofibrosarcoma Spindle Cell Variant Atypical Lipomatous Tumor
No lipoblasts Lipoblasts frequently present
Hypocellular Moderate cellularity
Perivascular grouping of cells No perivascular pattern
May have atypical mitotic figures No atypical mitotic figures
May have marked pleomorphism Mild to moderate atypia

MFH and other pleomorphic sarcomas vs Atypical Lipomatous Tumor

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