Liposarcoma is a rare type of cancer that develops in fat cells. It accounts for roughly 15% to 20% of all soft tissue sarcomas, making it one of the more common sarcomas, though sarcomas themselves represent less than 1% of all adult cancers. Liposarcoma most often grows in the deep soft tissues of the thigh or behind the abdominal organs (an area called the retroperitoneum), and it tends to affect adults between the ages of 40 and 60.
Types of Liposarcoma
Not all liposarcomas behave the same way. The World Health Organization recognizes several distinct subtypes, and knowing which one you’re dealing with matters because prognosis and treatment differ significantly.
Well-differentiated liposarcoma is the most common subtype, making up about 40% to 45% of cases. It grows slowly and rarely spreads to distant parts of the body. Under a microscope, the cells still look somewhat like normal fat cells. When this type occurs in the limbs, it carries an excellent outlook. When it develops in the retroperitoneum, it’s harder to remove completely and more likely to recur locally.
Dedifferentiated liposarcoma occurs when a well-differentiated tumor develops a more aggressive component. About 10% of well-differentiated liposarcomas will dedifferentiate over time. This subtype is more likely to recur and carries a higher risk of spreading to other organs, particularly the lungs.
Myxoid liposarcoma is the second most common subtype, accounting for roughly 30% of cases. It typically appears in the thigh and tends to affect younger adults compared to other subtypes. It has a distinctive genetic fingerprint: a translocation between chromosomes 12 and 16. When the tumor is purely myxoid without a “round cell” component, the prognosis is generally favorable. If round cells make up more than 5% of the tumor, it behaves more aggressively.
Pleomorphic liposarcoma is the rarest and most aggressive subtype. It grows quickly, has a high rate of metastasis, and carries the poorest prognosis of any liposarcoma type.
Where It Develops
The two most common locations are the extremities (especially the thigh) and the retroperitoneum, the space deep in the abdomen behind the intestines. Together, these sites account for the large majority of cases. Liposarcoma can also arise in the groin, behind the knee, or in the chest wall, though these locations are less common.
Retroperitoneal liposarcomas deserve special mention because they often grow very large before being discovered. The abdomen has room for a tumor to expand without causing obvious symptoms. Tumors reaching 20 centimeters or larger at diagnosis are not unusual in this location. By contrast, liposarcomas in the leg tend to be noticed earlier because a growing lump is harder to miss.
Symptoms and How It’s Found
The most common sign is a painless lump or swelling that gradually increases in size. In the limbs, you might notice a firm mass in the thigh that wasn’t there before. Pain occurs in roughly a third of cases, usually when the tumor grows large enough to press on nearby nerves or muscles.
Retroperitoneal tumors are sneakier. Symptoms tend to be vague: abdominal fullness, early satiety (feeling full after eating very little), weight gain in the midsection, or discomfort that’s easy to attribute to something else. Some people experience changes in bowel or urinary habits if the tumor presses on those structures. Many retroperitoneal liposarcomas are found incidentally during imaging for an unrelated issue.
A growing soft tissue mass larger than 5 centimeters, especially one that’s deep to the muscle layer rather than sitting just under the skin, raises suspicion. Superficial fatty lumps (lipomas) are extremely common and almost always benign, but a mass that is large, deep, firm, or rapidly growing warrants further investigation.
Diagnosis
Imaging is the first step. MRI is the preferred tool for tumors in the limbs because it provides detailed contrast between different soft tissues. CT scanning is typically used for retroperitoneal masses. Both can reveal characteristics that suggest liposarcoma, such as a mass with fatty components mixed with non-fatty, more solid areas.
A definitive diagnosis requires a tissue sample. A core needle biopsy, where a hollow needle extracts a small cylinder of tissue, is the standard approach for most suspected sarcomas. This provides enough material for a pathologist to determine the subtype. Open surgical biopsies are sometimes necessary for retroperitoneal tumors when needle biopsy results are inconclusive.
Pathologists use molecular and genetic testing to confirm the subtype. Well-differentiated and dedifferentiated liposarcomas show amplification of a specific region on chromosome 12. Myxoid liposarcomas carry their characteristic chromosomal translocation. These genetic markers help distinguish liposarcoma from benign fatty tumors and from other types of sarcoma.
Treatment Approaches
Surgery is the cornerstone of treatment for liposarcoma. The goal is to remove the entire tumor with a margin of healthy tissue around it. For tumors in the limbs, limb-sparing surgery is successful in the vast majority of cases. Amputation is rarely necessary with modern surgical techniques.
Radiation therapy is frequently used alongside surgery for extremity liposarcomas. It can be delivered before surgery (to shrink the tumor and make removal easier) or after surgery (to reduce the chance of local recurrence). For well-differentiated tumors that are completely removed with clean margins, radiation may not be needed. For higher-grade tumors or cases where margins are close, radiation plays a more important role.
Retroperitoneal liposarcomas present a greater surgical challenge. Complete removal often requires taking out adjacent organs, such as a kidney, part of the colon, or the spleen, because the tumor wraps around or adheres to these structures. Even with aggressive surgery, local recurrence rates in the retroperitoneum are high. Well-differentiated retroperitoneal liposarcomas have a local recurrence rate that can exceed 50% over the long term.
Chemotherapy has a limited role in most liposarcoma subtypes. Myxoid liposarcoma is the notable exception: it is more sensitive to chemotherapy than other subtypes, and treatment with certain drug combinations can produce meaningful tumor shrinkage. For dedifferentiated and pleomorphic liposarcomas, chemotherapy may be considered for tumors that have spread or cannot be surgically removed, though response rates are modest.
Outlook and Recurrence
Survival varies dramatically by subtype and location. Well-differentiated liposarcoma of the extremity has a 5-year survival rate above 90%. Even at 10 years, most patients with this subtype are alive and well, though continued surveillance is important because late recurrences can happen.
Dedifferentiated liposarcoma carries a 5-year survival rate closer to 50% to 70%, depending on the series. Pleomorphic liposarcoma has the worst outlook, with higher rates of metastasis and disease-related death.
Location matters as much as subtype. Retroperitoneal tumors of any subtype carry a worse prognosis than the same subtype in an extremity, largely because achieving complete surgical removal is more difficult and recurrence is more common. Patients with retroperitoneal liposarcoma often undergo multiple surgeries over the course of their disease.
The most common site of distant spread is the lungs. Myxoid liposarcoma has an unusual metastatic pattern: it tends to spread to other soft tissue sites, the spine, and the abdominal cavity before or instead of the lungs, which is different from most other sarcomas. This is why some oncologists recommend abdominal imaging in addition to chest imaging during follow-up for myxoid liposarcoma.
Risk Factors and Causes
For most people, there is no identifiable cause. Liposarcoma does not develop from benign lipomas. Despite the common concern, a lipoma you’ve had for years is not at risk of turning into liposarcoma. The two are biologically distinct.
Prior radiation exposure is one of the few recognized risk factors for soft tissue sarcomas in general. Sarcomas that develop in a previously irradiated field (called radiation-associated sarcomas) typically appear 8 to 15 years after radiation treatment. Certain rare inherited genetic conditions also increase sarcoma risk, but these account for a very small fraction of cases. Most liposarcomas arise spontaneously in people with no known risk factors.