Dedifferentiated Liposarcoma

Definition

Biphasic neoplasm with one component of atypical lipomatous tumor and a second component of high grade non-lipogenic sarcoma

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, non-lipogenic 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
Metastases contain only the non-lipogenic 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

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