Atypical Lipomatous Tumor
Supplemental Studies
Immunohistology
- p16 appears to be more sensitive for ALT/WDL than MDM2 or CDK4
- CDK4 may be more specific
- S100
- Fat cells positive
- Atypical cells and other cells negative
- CD34
- Atypical cells may be positive
- Occasional dendritic cells positive
- No widespread confluent positivity
- Actin, keratin negative
- MDM2 and CDK4 are markers amplified as a result of the supernumerary ring chromosomes described below
Immunohistochemistry of lipomatous tumors
| MDM2 | CDK4 | p16 | |
| Atypical lipomatous tumor | 45-100% | 84-92% | 78-97% |
| Dedifferentiated liposarcoma | 55-95 | 90-100 | 90 |
| Myxoid / round cell liposarcoma | 0-4 | 0-4 | 0 |
| Pleomorphic liposarcoma | 0 | 0 | 0 |
| Lipoma | 0-4 | 0-2 | 0 |
| Spindle cell and pleomorphic lipoma | 0-25 | 0-6 | 20 |
| Angiomyolipoma | 0 | 0 | |
| Hibernoma | 0 | 0 | positive, variable |
| Lipoblastoma | 0 (1 case) | 0 (1 case) | positive (1 case) |
Genetic analysis
-
>60% have supernumerary ring chromosomes derived from 12q(13-15)
- FUS/CHOP
t(12;16)(q13;p11) and EWS/CHOP t(12;22)(q13;q12) rare
- Common in myxoid liposarcoma
- FUS/CHOP
t(12;16)(q13;p11) and EWS/CHOP t(12;22)(q13;q12) rare
- 16q13 abnormality rare
- Common in spindle cell and pleomorphic lipomas
- FISH and quantitative PCR (QPCR) for MDM2 amplification can be utilized for diagnosis
- Appears useful for well differentiated lipomatous lesions vs lipoma
- May be less specific for high grade lesions
| MDM2 FISH | MDM2 QPCR | CDK4 FISH | CDK4 QPCR | |
| Atypical lipomatous tumor | 90-100% | 72-100% | 75-100% | 69-100% |
| Dedifferentiated liposarcoma | 100% | 100% | 100% | 100% |
| Myxoid liposarcoma | 20% | |||
| Spindle cell / pleomorphic lipoma | Negative | Negative | Negative | Negative |
| Angiolipoma | Negative | |||
| Lipoma, NOS | Negative | Negative | Negative | Negative |
| Sarcomas | 0-40% | 0% | 0% | 0% |
