Here is the typical myxoid liposarcoma appearance with delicate branching vasculature. Lipomatous differentiation is evident.
It transitions to more cellular areas where the neoplastic cells are obviously plumper and more crowded. We acknowledge the difficulty in accurately assessing the percentage of high grade areas, so it is important to consider any amount of hypercellularity as prognostically relevant.
Clusters of round cells are obvious here, surrounded by looser myxoid areas.
Myxoid and round cell liposarcoma are histologic spectrums of the same entity, and thus, are often referred to as myxoid/round cell liposarcoma. Up to half of liposarcomas are of this variety (Wu) and these lesions exhibit the t(12;16)(q13;p11) translocation which creates the CHOP-FUS fusion gene.
Tumors with pure myxoid liposarcoma are less aggressive (grade I of III), whereas those that exhibit round cell morphology are more aggressive (grade III of III). There is no consensus currently regarding the proportion of round cells seen in a myxoid liposarcoma for the entity to be called a myxoid/round cell liposarcoma. For some surgical pathologists, any focus of round cells is sufficient to designate the tumor as a myxoid/round cell liposarcoma. Prognostic cutoff values range from 5 to 30%. It is clear that more research needs to be conducted in this area.
One study found that retroperitoneal liposarcoma with morphological features suggestive of myxoid/round cell liposarcoma shows lack the characteristic FUS-CHOP or EWSR1-CHOP translocation suggesting this is actually a different entity (de Vreeze).
It is treated by wide surgical excision +/- adjuvant therapy. By comparison to other types of liposarcoma, this subtype has an unusually high response rate to adjuvant radiotherapy and chemotherapy (Jones).
1/3 of patients present with metastases (lungs, other soft tissue sites including pericardium, pleur, retroperitoneum and bone). In fact, it is this propensity to metastasis to other soft tissue sites that distinguished this subtype of liposarcoma from the other subtypes. Local recurrence occurs in about 10-14% although some studies report higher numbers. Overall disease specific survival is approximately 70% at 5 years and is related to the proportion of the round cell component.
Wu JM, Montgomery E. Classification and Pathology (of Soft Tissue Tumors). Surg Clin N Am 88 (2008) 483-520.
Jones RL, Fisher C, Al-Muderis O, and Judson IR. Differential sensitivity of liposarcoma subtypes to chemotherapy. European Journal of Cancer 2005, 41(18), 2853–2860.
de Vreeze RSA, et al. Primary retroperitoneal myxoid/round cell liposarcoma is a nonexisting disease: an immunohistochemical and molecular biological analysis. Modern Pathology 2009; 22, 223–231.