Round cell liposarcoma is a rare form of cancer that develops in the body’s fat cells, typically appearing in the arms and legs of people between the ages of 20 and 40. This condition can grow silently for years before producing noticeable symptoms, making early detection challenging but crucial for effective treatment.

Understanding Round Cell Liposarcoma

Round cell liposarcoma is actually part of a broader condition called myxoid/round cell liposarcoma, or MRCLS. This is one of several types of liposarcoma, which are cancers that begin in fat cells. The name “round cell” refers to how the cells appear when doctors examine them under a microscope, showing distinctive round or oval shapes. This type of tumor usually develops in the deep tissues of the body, particularly in the thighs, though it can appear in other parts of the arms and legs as well.^[1][2]

What makes round cell liposarcoma different from pure myxoid liposarcoma is the proportion of these round cells present. When more than 5% of the tumor consists of round cells, it is considered to have a round cell component. This distinction is important because tumors with a higher percentage of round cells tend to be more aggressive and have a greater likelihood of spreading to other parts of the body. While pure myxoid liposarcoma grows slowly, round cell liposarcoma can grow more quickly and poses greater challenges for treatment.^[4][6]

Who Gets Round Cell Liposarcoma

Round cell liposarcoma is extremely rare. In the United States, approximately 2,000 people are diagnosed with all forms of liposarcoma each year, and myxoid/round cell liposarcoma accounts for about 30% of these cases. This means that only a few hundred people receive this diagnosis annually. The condition can affect anyone, but it shows certain patterns in who it strikes most commonly.^[1][2]

Unlike many other types of cancer that primarily affect older adults, myxoid/round cell liposarcoma tends to appear in younger people. The typical age range for diagnosis is between 20 and 40 years old, though some sources note that the peak incidence occurs in people in their fourth to fifth decades of life, which is between ages 30 and 50. This makes it somewhat unusual compared to other liposarcoma types, which more commonly affect people between ages 50 and 65. The condition is rarely seen in children under 10 years old, though when liposarcoma does occur in children and adolescents, the myxoid type is the most common form.^[1][4][6]

Both men and women can develop round cell liposarcoma, with some studies showing no significant difference in occurrence between the sexes. However, other liposarcoma types typically affect men more than women, particularly those between ages 50 and 65. The global incidence of all soft tissue liposarcomas is estimated at approximately 2.5 per million people annually, highlighting just how rare these conditions truly are.^[5][6]

What Causes This Cancer

Scientists do not yet fully understand what causes round cell liposarcoma to develop. Like most cancers, it occurs when cells in the body undergo changes in their DNA that cause them to grow and multiply out of control. These abnormal cells accumulate to form tumors. However, what triggers these initial DNA changes remains unclear.^[2][9]

What researchers do know is that in most cases of myxoid/round cell liposarcoma, something very specific happens at the genetic level. About 90% of people with this condition have a characteristic chromosomal translocation, which means that pieces of two different chromosomes break off and swap places. Specifically, parts of chromosome 12 and chromosome 16 exchange positions, leading to the fusion of two genes called FUS and DDIT3 (sometimes referred to as CHOP).^[1][6]

This genetic fusion creates an abnormal hybrid protein called FUS-DDIT3. This hybrid protein disrupts normal cell processes in several ways. It interferes with how RNA is transcribed and causes problems with fat cell development and cell cycle control, which normally regulates when cells divide and when they stop dividing. When these processes malfunction, cells can transform from normal fat cells into cancer cells that multiply uncontrollably. While this genetic change happens in almost all cases, scientists are still working to understand exactly how this fusion protein causes cancer, hoping this knowledge will lead to new treatments.^[1][4][6]

It’s important to note that round cell liposarcoma is not known to run in families. You cannot inherit this condition from your parents, and having it does not mean your children will develop it. However, people with certain genetic conditions that increase cancer risk in general, such as Li-Fraumeni syndrome or neurofibromatosis, may have a higher risk of developing liposarcoma.^[1]

Risk Factors

Because the exact cause of round cell liposarcoma remains unknown, identifying clear risk factors is challenging. Unlike some cancers that have well-established risk factors such as smoking for lung cancer or sun exposure for skin cancer, there are no specific behaviors or exposures that are known to increase the risk of developing this particular cancer.^[2]

However, research has shown that people who have received radiation therapy for previous cancers have an increased risk of developing any kind of sarcoma, including myxoid liposarcoma. This doesn’t mean that everyone who receives radiation therapy will develop a sarcoma, but it does represent a known risk factor. The connection between radiation exposure and later sarcoma development suggests that damage to DNA from radiation may contribute to the cellular changes that lead to cancer.^[2]

Additionally, certain inherited genetic conditions can increase the overall risk of developing liposarcoma. Li-Fraumeni syndrome is a rare inherited condition that significantly increases the risk of developing several types of cancer, including sarcomas. Similarly, neurofibromatosis, which causes tumors to form on nerve tissue, is associated with an increased risk of certain sarcomas. These conditions are quite rare, and most people with round cell liposarcoma do not have these genetic syndromes.^[1]

Recognizing the Symptoms

One of the challenges with round cell liposarcoma is that many people have no symptoms at all when the cancer first starts to develop. These tumors can grow silently for several years without causing any noticeable problems. This is why the cancer is sometimes only discovered when it has already grown quite large or during an examination for something else entirely.^[1][2]

Eventually, as the tumor grows larger, symptoms begin to appear. The most common symptom is a visible lump or swelling under the skin, typically on the arm, leg, or particularly the thigh. Many people notice this lump because it keeps growing persistently rather than going away on its own like a bruise or minor injury would. The lump is often painless at first, which is why people sometimes wait before seeking medical attention.^[1][2]

Pain can develop if the tumor grows large enough to press on nearby nerves or other structures. Some people experience weakness in the affected arm or leg, or notice numbness in the area around the lump. As the tumor continues to grow, it may cause swelling in the surrounding area. Other symptoms can include feelings of tiredness or fatigue that doesn’t improve with rest, nausea, and unintentional weight loss. These more general symptoms typically appear in advanced cases or when the cancer has spread beyond its original location.^[1][2]

In some cases, myxoid/round cell liposarcoma can spread to unusual locations. While many cancers spread to the lungs, this type can spread to unusual soft tissue and bone locations. It may spread to fat pad areas in the back of the abdomen (retroperitoneum), trunk, the sac around the heart (pericardium), or the armpit. About one third of people with myxoid/round cell liposarcoma will experience metastatic disease, meaning the cancer spreads to other parts of the body. This can happen in multiple locations at the same time or at different times.^[6]

Prevention Strategies

Unfortunately, because the exact causes of round cell liposarcoma are not fully understood, there are no proven strategies to prevent this cancer from developing. Unlike some cancers where lifestyle changes such as not smoking or protecting skin from sun exposure can reduce risk, there are currently no known behaviors or habits that can prevent myxoid/round cell liposarcoma.^[1]

For people who have had radiation therapy as treatment for a previous cancer, being aware of the slightly increased risk of developing sarcomas is important. This doesn’t mean avoiding necessary radiation treatment, as the benefits of treating the original cancer far outweigh the small risk of developing a future sarcoma. However, it does mean that long-term monitoring and prompt attention to any new lumps or masses is particularly important for these individuals.^[2]

For people with genetic conditions such as Li-Fraumeni syndrome or neurofibromatosis, regular medical monitoring and screening may help detect cancers early when they are most treatable. These individuals should work closely with their healthcare providers to develop an appropriate surveillance plan based on their specific risk factors.^[1]

The best approach for everyone is to be aware of your body and seek medical attention if you notice any unusual changes, particularly lumps or swellings that persist or grow over time. While these symptoms are much more likely to be benign conditions rather than cancer, early evaluation allows for early detection if cancer is present, which typically leads to better treatment outcomes.^[2]

How the Body Changes with This Disease

Understanding what happens in the body when round cell liposarcoma develops helps explain both the symptoms people experience and how treatments work. At the cellular level, the disease begins when normal fat cells undergo genetic changes that transform them into cancer cells. This transformation is driven by the FUS-DDIT3 fusion protein that disrupts normal cellular functions.^[1][4]

Normal fat cells, called adipocytes, develop through a carefully regulated process where immature cells gradually mature into fully formed fat cells. The FUS-DDIT3 fusion protein interferes with this maturation process, preventing fat cells from developing normally. Instead, cells remain in an immature state and begin multiplying uncontrollably. These abnormal cells are sometimes called lipoblasts, which are immature fat cells characterized by a hyperchromatic nucleus (darkly staining center) that appears indented or scalloped by fat in the cytoplasm.^[5][6]

When examined under a microscope, myxoid/round cell liposarcoma has a distinctive appearance. The tumor is composed of uniform round to oval-shaped primitive cells and small lipoblasts embedded in a prominent myxoid stroma, which is a jelly-like substance. The tumor also features a characteristic network of branching capillaries (tiny blood vessels) that has been described as having a “chicken wire” or plexiform pattern. In tumors with a significant round cell component, there are more densely packed round cells that give these tumors their name and more aggressive behavior.^[4][5][6]

As the tumor grows, it typically forms large, well-defined masses within muscles. When surgeons examine these tumors, they often appear as multinodular (having multiple rounded sections) with a smooth, gelatinous, glistening surface in lower-grade tumors. Higher-grade tumors with more round cells tend to have a firmer, more fleshy appearance. The tumors usually do not show visible areas of tissue death (necrosis) on their surface.^[4]

The tumor cells grow slowly in most cases, which is why symptoms may not appear for years. However, tumors with a higher percentage of round cells grow more quickly. As the mass enlarges, it begins to press on surrounding tissues. If it presses against nerves, it causes pain or numbness. If it compresses blood vessels, it may affect circulation. If it grows large enough to press against muscles, it can cause weakness or difficulty moving the affected limb.^[2]

Unlike many other cancers that primarily spread to the lungs, myxoid/round cell liposarcoma has an unusual pattern of spread. It tends to metastasize to other soft tissue locations and bones rather than following typical cancer spread patterns. This unusual behavior reflects the specific biology of this cancer type and requires doctors to look for spread in different locations than they might for other cancers.^[2][6]