Dedifferentiated Liposarcoma
Definition
- Biphasic neoplasm with one component of atypical lipomatous tumor and a second component of high grade sarcoma
Diagnostic Criteria
- Biphasic neoplasm
- Both components may be present in one specimen
- Components may be adjacent or intermingled
- Proposed size requirement for high grade component is one 10x objective field
- May be temporally biphasic with a high grade non-lipogenic recurrence in a patient with an atypical lipomatous tumor
- One component must be atypical lipomatous tumor
- Mature fat and atypical cells
- Other component must be high grade sarcoma
- Mitotic rate at least 5/10 hpf
- Cytologically obvious sarcoma does not have a required mitotic rate
- Pleomorphic MFH pattern is most common
- Many other types of sarcoma may be seen
- Classically the sarcoma must be non-lipogenic
- Recent studies describe cases that appear to represent dedifferentiation as pleomorphic liposarcoma (Boland 2010, Mariño-Enríquez 2010)
- Classically the sarcoma must be non-lipogenic
- An inflammatory myofibroblastic tumor component has been proposed as dedifferentiation
(Lucas, 2010)
- None of the cases with only IMT in the dedifferentiated component metastasized, thus this does not appear to qualify
- Mitotic rate at least 5/10 hpf
- A high grade sarcoma arising in a location typical of atypical lipomatous tumor (such as retroperitoneum) that is FISH positive for amplification of MDM2 may also be considered a dedifferentiated liposarcoma
- Both components may be present in one specimen
- Metastases contain only the high grade sarcoma component
- By definition, may not occur following radiation of atypical lipomatous tumor
- Low grade dedifferentiated liposarcoma has been proposed
- Non-lipogenic component with features of fibromatosis, low grade fibrosarcoma or dermatofibrosarcoma protuberans
- Mitotic rate <5/10 hpf
- Survival is the same as atypical lipomatous tumor
- All cases that metastasized had a local recurrence with a high grade component or were incompletely resected
- We do not make this diagnosis
- Cellular atypical lipomatous tumor (Evans 2007) is an acceptable term
- Non-lipogenic component with features of fibromatosis, low grade fibrosarcoma or dermatofibrosarcoma protuberans
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
Original posting/last update : 8/4/07, 4/16/12
