A dedifferentiated liposarcoma is a soft tissue tumour which shows progression either in the primary tumour or after local recurrence to a sarcoma of variable histological grade, often not lipogenic. Dedifferentiated liposarcoma occurs in up to 10% of well-differentiated liposarcomas, although the risk is higher in the retroperitoneum and lower in the extremities, likely reflecting the longer time taken to detect tumours in the former location.
Dedifferentiated liposarcomas are most common in the retroperitoneum, but can occur in the spermatic cord or rarely head and neck and trunk. They are extremely rare in subcutaneous tissues. These tumours usually present as a painless mass, with both lipomatous and non-lipomatous elements on MRI scanning. Some present with an increase in size of a long-standing tumour, suggestive of dedifferentiation.
Dedifferentiated areas are variable histologically, but can resemble undifferentiated pleomorphic sarcoma or myxofibrosarcoma. Tumours most often contain ring or giant marker chromosomes.
After treatment, local recurrence can occur in up to 40% of cases, particularly in the retroperitoneum. Tumours exhibit a less aggressive clinical course than other types of high grade pleomorphic sarcoma, with metastases in 15-20% of cases and a overall mortality of 28-30% at 5 years.
1. WHO Classification of Tumours of Soft Tissue and Bone. 4th Edition, 2013.