Round Cell Liposarcoma

Round cell liposarcoma is a rare cancer that develops in fat cells, usually appearing as a slow-growing lump in the arms or legs, most commonly affecting people between the ages of 20 and 40.

Table of contents

• What is round cell liposarcoma?
• Medical identification codes
• Other names for this condition
• How common is it?
• Who is affected?
• Where does it occur in the body?
• Signs and symptoms
• How is it diagnosed?
• What causes this cancer?
• Does it run in families?
• Treatment options
• What to expect

What is round cell liposarcoma?

Round cell liposarcoma is a type of cancer that begins in the body’s fat cells. It is actually a subtype of myxoid liposarcoma, which is why healthcare providers often call it myxoid/round cell liposarcoma or MRCLS^[1]. The term “round cell” describes how the cancer cells look when doctors examine them under a microscope^[2].

This cancer is part of a larger group of rare cancers called liposarcoma, which all start in fat tissue. Round cell liposarcoma usually develops in the arms and legs, most commonly in the thighs^[1]. While myxoid liposarcoma typically grows slowly, tumors with a significant round cell component tend to be more aggressive. When round cells make up more than 5% of the tumor, it is considered a higher-grade cancer with a greater chance of spreading to other parts of the body^[4].

Medical identification codes

C49.9
D018208
ORPHA:99967; OMIM:613488; UMLS:C0206634

Other names for this condition

Myxoid/round cell liposarcoma, MRCLS, round cell liposarcoma

How common is it?

Round cell liposarcoma is extremely rare. In the United States, about 2,000 people are diagnosed with all types of liposarcoma each year. Myxoid/round cell liposarcoma together make up about 30% of all liposarcoma cases^[1]. This means that only a few hundred people in the United States receive this diagnosis annually. The condition accounts for approximately 20 to 30% of liposarcomas and about 5% of all adult soft tissue sarcomas, which are cancers that develop in the body’s connective tissues^[4].

Who is affected?

Round cell liposarcoma typically affects people between the ages of 20 and 40, which is younger than most other types of liposarcoma^[1]. Some sources indicate the typical age range for diagnosis is between 35 and 55 years^[6]. While it can occur in children and adolescents, it is rarely seen in children under 10 years old^[1]. The condition appears to affect men and women at roughly equal rates, with no significant difference between sexes^[4].

Where does it occur in the body?

• Arms and legs (especially thighs)
• Deep soft tissues
• Muscles
• Skin and nearby soft tissue
• Bones (pelvic bones, spine)
• Heart
• Lungs
• Esophagus
• Retroperitoneum (back of abdomen)
• Pericardium

Round cell liposarcoma most commonly develops in the deep soft tissues of the arms and legs, particularly in the thigh^[4]. The tumors can spread to nearby soft tissue, including muscle and skin. In some cases, the cancer can also appear in bones such as the pelvic bones or spine, or in organs including the heart, lungs, or esophagus^[2].

About one third of cases will spread to unusual locations, with tumors appearing in multiple sites at the same time or at different times. These can include fat pad areas in the back of the abdomen, trunk, the sac around the heart, and underarm areas^[6]. Very rarely, these tumors can arise as primary tumors in the layer of fat just beneath the skin or in the retroperitoneum, which is the space at the back of the abdomen^[4].

Signs and symptoms

Many people with round cell liposarcoma do not notice any symptoms when the cancer first starts. The tumor can be present for several years before it grows large enough to cause problems^[2]. Most often, the first sign is a large, painless lump or mass in the affected area^[4].

When symptoms do appear, they may include:

• A visible lump under the skin that continues to grow
• Pain in the affected area
• Swelling or numbness around the lump
• Weakness in the affected arm or leg
• Tiredness or fatigue
• Nausea
• Unintentional weight loss^[1]

The symptoms can vary depending on where the tumor is located and how large it has grown. A liposarcoma may cause pain if it presses on a nerve, and it may affect the function of nearby organs^[16].

How is it diagnosed?

Diagnosing round cell liposarcoma involves several steps. Your doctor will start with a physical examination, looking at and feeling any lump you may have noticed^[20].

Imaging tests are an important next step. Your doctor will use scans to look at where the tumor is located and how big it is. These tests also help check whether the cancer has spread to other parts of the body^[1]. Common imaging tests include:

• CT scans (computed tomography): These create detailed images that help doctors see how close tumors are to major organs and evaluate tumor size^[2]
• MRI scans (magnetic resonance imaging): These help doctors check on nearby nerves, blood vessels, and muscles that the tumor may affect^[2]

To confirm the diagnosis, your doctor will perform a biopsy. During this procedure, a small sample of tissue is taken from the tumor with a needle. An expert called a pathologist then studies the cells from the sample under a microscope to determine what kind of tumor it is^[1]. For tumors in the arms and legs, doctors generally take multiple core biopsies to identify whether the tumor has a myxoid or round cell component and to stage the disease^[6].

Molecular and genetic testing can confirm whether a tumor is truly a round cell liposarcoma. These tests look for specific genetic changes in the tumor cells^[2]. The diagnosis can be confirmed by finding evidence of a specific genetic change involving the DDIT3 and FUS genes, which can be detected using specialized laboratory techniques^[6].

It is important for doctors to determine how much of the tumor is made up of round cells, because having more than 5% round cells predicts a poorer outcome^[6].

What causes this cancer?

Scientists do not yet know exactly what causes round cell liposarcoma to form. Like most cancers, it occurs when cells in the body change and grow out of control^[9]. Medical researchers do know that most people with this condition carry a genetic change that turns normal genes into oncogenes, which are genes that can cause cancer^[2].

In most cases of round cell liposarcoma, a chromosome (the structure in your cells that contains your genes) breaks apart and gets put back together in the wrong way. This can cause cells to not function as they should^[1]. About 90% of these tumors have a characteristic change in the chromosomes that leads to the joining of two genes: a gene called FUS and a gene called DDIT3 (also known as CHOP). These genes are normally found on different chromosomes, but in this cancer they become fused together^[6].

The result is the creation of a hybrid protein that disrupts normal cell processes. This abnormal protein interferes with how cells read and use genetic information, and it prevents fat cells from maturing properly, which promotes cancer development^[6]. This genetic change happens in almost all cases of myxoid/round cell liposarcoma, so scientists believe it may be very important for how this cancer forms^[1].

While researchers do not know what specifically causes these genetic changes, studies show that people who have had radiation therapy for cancer have an increased risk of developing any kind of sarcoma, including myxoid liposarcoma^[2].

Does it run in families?

Round cell liposarcoma is not known to run in families^[1]. However, if you have this condition, you may have other inherited conditions that increase your chance of getting cancer. Genetic conditions such as Li-Fraumeni syndrome and neurofibromatosis may increase your risk of getting liposarcoma^[1].

Treatment options

Treatment for round cell liposarcoma will be unique for each patient. It is important to see an expert who specializes in liposarcoma treatment to decide the best approach for your specific tumor^[1]. Treatment options may include surgery, radiation therapy, chemotherapy, or a combination of these approaches.

Surgery is often the main treatment. The surgeon will remove the tumor and will try to take out an area of normal tissue around it as well. This is called taking a margin, and it allows any cancer cells that are not visible to the naked eye to be removed along with the tumor. This can reduce the risk of the cancer coming back^[20]. The goal is to remove the tumor while trying to avoid removing healthy tissue^[1]. In rare cases, surgical amputation of the limb may be necessary^[6].

Radiation therapy uses high-energy rays to kill cancer cells. It can be used around the time of surgery to shrink the tumor so it can be removed more easily. Radiation therapy can also be used after surgery if there is concern that tumor cells remain^[1]. Round cell liposarcoma responds particularly well to radiation therapy compared to other types of sarcoma^[4].

Chemotherapy uses drugs to kill cancer cells throughout the body. For cases that are difficult to treat with surgery alone, or when the cancer has spread to other parts of the body, chemotherapy can be used to treat the tumor^[1]. High-grade round cell liposarcoma that is large (more than 5 centimeters) or difficult to remove completely may be treated with chemotherapy before surgery, after surgery, or both^[6]. Round cell liposarcoma is relatively sensitive to certain chemotherapy drugs, particularly those called anthracyclines (such as doxorubicin) and ifosfamide, which are usually first-line treatment options. Another drug called trabectedin (also known as ecteinascidin) is used as a second-line treatment^[6].

What to expect

The estimate of how a disease will affect you in the long term is called prognosis. Every person is different, and prognosis depends on many factors^[1], including:

• Where the tumor is located in your body
• Whether the cancer has spread to other parts of your body
• How much of the tumor was removed during surgery
• The percentage of round cells in the tumor^[1]

The presence of a high level of round cells in the tumor predicts a poorer outcome^[6]. Additional factors that may indicate a worse prognosis include the tumor’s location, a high rate of cell division noted on testing, and certain genetic changes in the cancer cells^[15].

For patients with myxoid/round cell liposarcoma that is small and has not spread to other parts of the body, the 5-year survival rate is over 80%^[1]. However, about one third of all cases will develop metastasis, which means the cancer spreads to other locations in the body. These tumors can spread to unusual bone and soft tissue locations^[6].

After treatment, you will need regular follow-up care to make sure the tumor does not grow back. Follow-up appointments will typically include a chance to discuss symptoms, an examination to look for signs of the cancer returning, and imaging tests such as MRI or ultrasound if needed. You will also have chest X-rays to check for any secondary cancers in the lungs^[20]. Lifelong follow-up is recommended^[6].

If the cancer does come back, it is important to get treated as quickly as possible^[20]. If you want information about your specific prognosis, it is important to talk to your doctor, who knows your individual situation^[1].