Liposarcomas
Liposarcomas are a type of malignant soft-tissue tumor that primarily affects adults, classified as one of the more common subtypes of soft-tissue sarcomas. There are three main subtypes recognized by the World Health Organization: well-differentiated and dedifferentiated liposarcoma, myxoid and round cell liposarcoma, and pleomorphic liposarcoma. These tumors can occur in various locations, including the abdomen, thighs, legs, arms, or buttocks, often presenting as large, painless masses. Liposarcomas account for approximately 20 percent of all malignant soft-tissue tumors, with an incidence of 2.5 cases per million people annually.
While the well-differentiated subtype has a more favorable prognosis, the other types, particularly the pleomorphic and round-cell variants, tend to have higher recurrence rates and poorer survival outcomes. Diagnosis typically relies on imaging techniques such as MRI, which can reveal hypervascular masses, and treatment generally involves surgical resection, with additional therapies like radiation or chemotherapy used for higher-stage tumors. Understanding liposarcomas is crucial for timely diagnosis and management, as symptoms may include weight loss, abdominal discomfort, and other systemic signs due to tumor growth.
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Subject Terms
Liposarcomas
ALSO KNOWN AS: Soft-tissue liposarcomas
RELATED CONDITIONS: Soft-tissue sarcomas
DEFINITION: Liposarcomas are among the most common subtypes of malignant soft-tissue sarcomas in adults after malignant fibrous histiocytoma (MFH). The World Health Organization recognizes three subtypes of liposarcomas—well-differentiated and dedifferentiated liposarcoma (WDLPS/DDLPS), myxoid and round cell liposarcoma (MLS and RCL), and pleomorphic liposarcoma (PLS).
Liposarcoma, a mesenchymal sarcoma, accounts for 20 percent of all malignant soft-tissue tumors and usually manifests as a nonspecific soft-tissue mass in the abdomen, thigh, legs, arms, or buttocks. Frequently, the fat it contains is not radiographically detectable. Liposarcoma demonstrates a wide range of manifestations and prognoses, ranging from a well-differentiated non-metastasizing neoplasm with a good prognosis to a high-grade sarcoma with hematogenous metastases to the lung and the visceral organs.
Risk factors: A relationship to trauma has been reported. The myxoid and round-cell type of liposarcoma are associated with a reciprocal translocation between chromosomes 12 and 16. The average age at diagnosis is fifty.
Etiology and the disease process: Liposarcoma is a malignant tumor of mesenchymal origin made up of several cell types with the microscopic appearance of adipose tissue, although it does not contain visible fat in some cases. The well-differentiated type of liposarcoma has the best prognosis and has mature lipocytes with varying degrees of nuclear atypia. It is seen in only 15 percent of cases. The most common type, accounting for 40 to 50 percent of all liposarcomas, is myxoid, composed of proliferating fibroblasts with less than 10 percent fat. This type of tumor often metastasizes to serosal and pleural surfaces, subcutaneous tissue, and bone. The pleomorphic type is seen in approximately 20 percent of cases and is a highly anaplastic tumor with pleomorphic (many-sized and shaped) cells growing disorderly. The round-cell type is seen in less than 10 percent of cases, is poorly differentiated, and is often associated with hemorrhage and necrosis. It is highly cellular, composed of primitive small round cells. Retroperitoneal liposarcoma is a slow-growing variant that rarely metastasizes and usually displaces rather than infiltrates or invades surrounding tissues.
Incidence: Liposarcomas represent between 12 and 18 percent of all malignant soft-tissue tumors, and annually, 2.5 cases occur per one million population.
Symptoms: Liposarcoma usually manifests as a large, painless mass between 2 and 30 centimeters (cm) in size, associated with weight loss in a patient between the ages of fifty and sixty. It is slightly more common in men than women. Liposarcoma can be painful because of the compression of the adjacent neurovascular bundle or adjacent abdominal organs. Retroperitoneal tumors can weigh several pounds. Other symptoms include constipation, swelling, blood in stool, stomach cramps, and vomiting.
Screening and diagnosis: Liposarcomas are best diagnosed by magnetic resonance imaging (MRI) with gadolinium intravenous contrast. The tumor appears as a large hypervascular septated mass containing fat and soft tissue. In contradistinction to a lipoma, liposarcoma enhances with intravenous contrast. Liposarcoma can have large areas of necrosis and hemorrhage and can be located in the trunk or retroperitoneum in approximately 42 percent of cases, in the lower extremities in 41 percent of cases, in the upper extremities 11 percent of the time, and in the head and neck in 6 percent of cases, with a predilection for the thigh and retroperitoneum. The more differentiated the tumor, the closer the signal characteristics of the tumor approach that of fat. Myxoid and pleomorphic tumors may demonstrate little or no fat on computed tomography (CT) scans. On nuclear medicine positron emission tomography (PET) scans, the tumor is fluorodeoxyglucose (FDG) avid.
The most common type, the myxoid type (50 percent of all liposarcomas), can appear benign on MRIs. These gelatinous lesions can demonstrate a cystlike appearance. High-grade liposarcoma often contains no recognizable fat and is indistinguishable from other soft-tissue malignancies.
As with most malignant musculoskeletal tumors, surgical staging depends on pathology, compartmentalization, and the presence or absence of metastases:
- Stage Ia: Low grade, intracompartmental
- Stage Ib: Low grade, extracompartmental
- Stage IIa: High grade, intracompartmental
- Stage IIb: High grade, extracompartmental
- Stage IIIa: Low or high grade, intracompartmental, presence of metastases
- Stage IIIb: Low or high grade, extracompartmental, presence of metastases
Treatment and therapy: The treatment depends on the stage at diagnosis. Stage I lesions are handled with surgical resection with wide margins. Stage II lesions are treated with more radical resection, possible amputation, and radiation therapy. Therapy for Stage III lesions includes surgical resection with radiation and chemotherapy.
Prognosis, prevention, and outcomes: The well-differentiated type of liposarcoma has the best prognosis, with five-year survival rates exceeding 80 percent and a reoccurrence rate of 50 percent. The well-differentiated type rarely metastasizes. The pleomorphic and round-cell types metastasize more often, with a recurrence rate of over 80 percent. The five-year survival rate of pleomorphic and round-cell types is around 50 percent, with most living 4 to 104 months after diagnosis. A size greater than 15 centimeters connotes a poor prognosis. Retroperitoneal liposarcoma is the most radiosensitive of all soft-tissue sarcomas, with an overall five-year survival of 32 percent.
Bibliography
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