Atypical Spindle Cell Lipomatous Tumor

Definition

Lipomatous tumor composed of mild to moderately atypical spindle cells intermixed with variably atypical fat cells

Variable combination of atypical spiindle cells admixed with atypical lipocytes
- Nearly always intimately admixed
  - Broad range of proportions
- Spindle cells uniformly mildly to moderately atypical
- Predominantly mature adipose tissue
  - Frequently shows variablecell size
  - Lipoblasts present in about half of cases
- Scattered large bizzare hyperchromatic cells may be present in both spindle and adipose component
- Mitotic figures very rare
Extracellular matrix frequently abundant
- May be myxoid or collagenous
  - Ropey collagen not prominent
- Rarely may show dystrophic calcification, ossification or muxcle differentiation
Lobular pattern, may be circumscribed or infiltrative

IPOX studies
- CD34 positive approximately 65%
- S100 both spindle and adipose cells 40%
- Desmin positive spindle cells approximately 20%
- MDM2 and CDK4 faint and focal in 5%
FISH negative for MDM2
- Should be performed on all questioinable cases
Giant ring chromosomes not seen

Nealy all over age 30
- Median age mid 50's
- Range 6-87
Predominantly on extremities and limb girdles
- Rare sites include mediastinum, retroperitoneum, abdomen
About 10% recurrence rate
- May be multiple and late
- No aggressive recurrences or destructive growth
No reported dedifferentiation or metastases

Spindle Cell Lipoma	Atypical Spindle Cell 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 5% reactive
Rb loss in all cases	Rb normally expresed in 40$

MDM2 and CDK4 negative to weak focal in 5% (FISH negative)

Neurofibroma with Fat Component	Atypical Spindle Cell Lipomatous Tumor
Hypocellular	Moderate cellularity
Wavy nuclei	Spindled, nonwavy nuclei
No nuclear pleomorphism	Mild to moderate atypia
May be seen in children	Rare under 30
Poorly circumscribed	May be circumscribed

Dermatofibrosarcoma Protuberans	Atypical Spindle Cell Lipomatous Tumor
No cytologic atypia	Mild to moderate atypia
Entrapped fat at periphery	Fat integral to lesion
No lipoblasts	Lipoblasts frequently present

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

Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Original posting : July 29, 2007
Last update: 3/14/16