Myxoid Liposarcoma: Understanding Your Pathology Report

by Bibianna Purgina, MD FRCPC
April 10, 2026

Myxoid liposarcoma is a type of cancer that starts in fat cells. It is classified as a sarcoma — a cancer arising from the connective tissues of the body — and more specifically as a type of liposarcoma, meaning a sarcoma of fat tissue. Myxoid liposarcoma most commonly develops in the deep soft tissues of the thigh, though it can arise anywhere in the body. It typically affects adults between the ages of 30 and 50, making it one of the more common liposarcomas in younger adults. Many patients receive radiation therapy before surgery to shrink the tumor and improve the chances of complete removal.

This article will help you understand the findings in your pathology report — what each term means and why it matters for your care.

What causes myxoid liposarcoma?

Almost all myxoid liposarcomas are caused by a specific genetic change called a translocation. A translocation occurs when a piece of one chromosome breaks off and attaches to a different chromosome, creating an abnormal fusion gene. In myxoid liposarcoma, this translocation fuses the DDIT3 gene with either the FUS or EWSR1 gene. The resulting abnormal fusion protein disrupts normal fat cell maturation and drives them to grow uncontrolled. At present, doctors do not know what triggers this translocation to occur in the first place.

What are the symptoms?

Most myxoid liposarcomas present as a large, painless lump or mass, most often in the thigh. Because the tumor typically grows in deep tissue beneath the muscle, it can reach a considerable size before it is noticed — patients and their doctors may not feel it until it becomes quite large. Tumors located deep in the abdomen may go undetected even longer, until the mass causes pressure symptoms such as abdominal discomfort or fullness. Pain, numbness, or weakness in the affected limb can occur if the tumor grows large enough to press on nearby nerves or blood vessels.

How is the diagnosis made?

The diagnosis is made after a tissue sample is examined under the microscope by a pathologist. The sample is usually obtained through a core needle biopsy, in which a hollow needle removes small cylinders of tissue from the tumor. In some cases, the entire tumor is surgically removed first, and the diagnosis is made on the excision specimen.

Under the microscope, myxoid liposarcoma has a distinctive appearance. The tumor cells are embedded in an abundant pale, gel-like background called myxoid matrix — a loose, water-rich material that gives the tumor its name. Scattered throughout this matrix are immature fat cells called lipoblasts, which are fat cells that have not fully matured. Lipoblasts have a distinctive appearance: they contain one or more small fat droplets inside the cell that push the nucleus to the side. A defining feature of myxoid liposarcoma is a delicate network of small branching blood vessels that pathologists describe as having a “chicken-wire” or plexiform pattern. This vascular pattern, combined with the myxoid matrix and lipoblasts, is characteristic of this tumor type.

An important additional feature to recognize is the round cell component. In some myxoid liposarcomas, areas of the tumor contain densely packed, small round cells with little surrounding matrix — these are called round cells and represent a higher-grade component of the tumor. The percentage of round cells present has direct implications for grade and prognosis (see Histologic grade below).

To confirm the diagnosis, the pathologist performs molecular testing to detect the characteristic DDIT3 gene rearrangement. This is done using fluorescence in situ hybridization (FISH) — a test that uses fluorescent probes to detect the translocation — or next-generation sequencing (NGS), which reads large stretches of DNA to identify the fusion gene. Either test can be performed on the biopsy specimen or on the surgically removed tumor. A positive result confirms the diagnosis and helps rule out other soft-tissue tumors that can appear similar under the microscope. Once the diagnosis is confirmed, imaging — typically MRI of the primary tumor site and CT of the chest, abdomen, and pelvis — determines the full extent of disease.

Histologic grade

Pathologists assign a grade to myxoid liposarcoma using the FNCLCC grading system (French Federation of Cancer Centers Sarcoma Group). This system scores three microscopic features — tumor differentiation, mitotic count, and necrosis — and adds the scores together to determine the final grade. Higher-grade tumors grow faster, are more likely to spread to other parts of the body, and are associated with a worse prognosis.

The three scored features are:

• Tumor differentiation — This describes how closely the tumor cells resemble normal fat cells. Myxoid liposarcoma with predominantly myxoid features and typical lipoblasts receives a score of 2 (moderately differentiated). Tumors with a significant round cell component are given a higher differentiation score of 3.
• Mitotic count — A mitotic figure is a cell caught in the act of dividing. The pathologist counts the number of mitotic figures in 10 areas of the most active part of the tumor. Tumors with very few dividing cells (0–9 per 10 fields) receive 1 point; those with 10–19 receive 2 points; those with 20 or more receive 3 points.
• Necrosis — Necrosis is a type of cell death. Fast-growing tumors may outgrow their blood supply, causing areas of the tumor to die. No necrosis = 0 points; necrosis in less than 50% of the tumor = 1 point; necrosis in 50% or more of the tumor = 2 points.

The total score determines the FNCLCC grade:

• Grade 1 — Total score 2 or 3. Low-grade tumor. Tends to grow slowly and is less likely to spread.
• Grade 2 — Total score 4 or 5. Intermediate-grade tumor.
• Grade 3 — Total score 6 to 8. High-grade tumor. More aggressive and more likely to spread to other parts of the body.

For myxoid liposarcoma specifically, the proportion of round cells is an important additional grading consideration. When more than 5% of the tumor is made up of round cells, this is associated with more aggressive behavior and a worse prognosis, regardless of the overall FNCLCC score. Your report may describe the tumor as myxoid/round cell liposarcoma when a significant round cell component is present. When more than 80% of the tumor is round cells, the tumor is considered high grade. Your pathologist will note the estimated percentage of round cells in the report.

Tumor size

Tumor size is measured at its greatest dimension in centimeters. Larger tumors are more likely to spread to other parts of the body and are associated with a worse prognosis. Tumor size is also used to determine the pathologic tumor stage (pT) — in most body sites, tumors smaller than 5 cm are lower stage than larger tumors. The final measurement is taken from the surgically removed specimen, not from a biopsy.

Tumor extension

Myxoid liposarcoma typically arises deep within a muscle or other soft-tissue compartment. As the tumor grows, it can spread beyond its original location into surrounding structures. This is called tumor extension. Your pathologist will carefully examine all tissue submitted from the surgical resection to determine whether tumor cells have grown into adjacent muscles, organs, bones, blood vessels, or nerves. The extent of tumor extension is used to assign the pathologic tumor stage (pT). Tumors that remain confined to their original compartment are lower stage than those that have spread into adjacent structures.

Treatment effect

Many patients with myxoid liposarcoma receive radiation therapy and/or chemotherapy before surgery — a strategy called neoadjuvant therapy — to shrink the tumor and make complete surgical removal more achievable. After surgery, the pathologist examines the entire specimen to determine how much of the tumor responded to treatment.

The pathologist estimates the percentage of the tumor that is non-viable — meaning dead — versus viable — meaning still alive. A high percentage of non-viable tumor (typically 90% or more) indicates a good response and is generally associated with a better outlook. A low percentage of non-viable tumor indicates that the tumor did not respond well to pre-operative treatment, which may influence decisions about further therapy. Your pathology report will describe the estimated percentage of viable and non-viable tumor.

Lymphovascular invasion

Lymphovascular invasion means that tumor cells are present inside blood vessels or lymphatic channels within or around the tumor. Lymphatic vessels carry fluid toward nearby lymph nodes, and blood vessels circulate throughout the body — when tumor cells enter either, they have a route to spread to lymph nodes or distant organs. Lymphovascular invasion is uncommon in myxoid liposarcoma, but when present, it is noted in the report as an adverse feature. Its presence increases the risk of spread and may influence decisions about additional treatment.

Perineural invasion

Perineural invasion means that tumor cells are growing along or around a nerve. Nerves run throughout the soft tissues, and tumor cells that reach them can use the nerve as a pathway to spread into surrounding tissues beyond the main tumor mass. This increases the risk that the tumor will grow back in the same area after surgery. Your pathology report will state whether perineural invasion was identified.

Surgical margins

A margin is the edge of the tissue removed during surgery. For soft tissue sarcomas, margins are critically important because the goal of surgery is to remove the entire tumor with a rim of normal tissue around it. The pathologist examines all cut surfaces of the resection specimen to determine whether tumor cells are present at the edges.

• Negative margin — No tumor cells are present at the cut edge. This suggests the tumor was completely removed. In sarcoma surgery, the distance from the tumor to the nearest margin — even when negative — may be measured and reported, as a wider margin is associated with a lower risk of tumor recurrence.
• Positive margin — Tumor cells are present at the cut edge, meaning some tumor may remain in the body. A positive margin significantly increases the risk of local recurrence (the tumor growing back in the same area) and may lead to a recommendation for further surgery or additional radiation therapy.

Depending on the location and extent of the surgery, margins may be named in the report (e.g., deep, superficial, or medial margins). All named margins will be described as negative or positive.

Lymph nodes

Lymph nodes are small immune organs located throughout the body. Cancer cells can spread from a tumor to nearby lymph nodes through lymphatic vessels — a process called metastasis. Lymph node involvement is uncommon in myxoid liposarcoma compared to many other cancers, and lymph nodes are not routinely removed during surgery unless they appear enlarged or suspicious on imaging.

If lymph nodes were removed as part of your surgery, your pathology report will state the total number examined and whether any contain tumor cells. Lymph node involvement (pN1) increases the stage of the cancer and is an adverse prognostic finding.

Biomarker and molecular testing

For most patients with myxoid liposarcoma, there are currently no established biomarker tests that directly guide treatment decisions in the way that HER2 or MMR testing does in other cancers. The DDIT3 gene rearrangement used to confirm the diagnosis (described under “How is the diagnosis made?” above) is a diagnostic molecular test rather than a treatment-guiding biomarker.

Research into molecular targets in myxoid liposarcoma is ongoing. In selected patients with advanced or recurrent disease, molecular profiling using next-generation sequencing (NGS) may be performed to identify additional genetic changes that could inform clinical trial eligibility or potential targetable alterations. Your oncologist will discuss whether molecular profiling is appropriate in your case. For more information about biomarker testing in cancer, visit our Biomarkers and Molecular Testing section.

Pathologic stage (pTNM)

The pathologic stage is determined from the surgical specimen and describes how far the cancer has spread. It uses the internationally recognized TNM staging system, which considers the primary tumor (T), lymph node involvement (N), and distant metastasis (M). Higher numbers indicate more advanced disease. Metastasis to distant organs is typically determined by imaging rather than by the pathologist.

The tumor stage (pT) for soft tissue sarcomas varies depending on the body part where the tumor started. The staging criteria for the most common locations are listed below.

Tumor stage (pT)

Trunk and extremities (chest wall, abdomen, arms, legs) — most common location for myxoid liposarcoma:

• pT1 — Tumor is 5 cm or smaller.
• pT2 — Tumor is more than 5 cm but 10 cm or smaller.
• pT3 — Tumor is more than 10 cm but 15 cm or smaller.
• pT4 — Tumor is more than 15 cm.

Retroperitoneum (deep abdominal cavity behind the organs):

• pT1 — Tumor is 5 cm or smaller.
• pT2 — Tumor is more than 5 cm but 10 cm or smaller.
• pT3 — Tumor is more than 10 cm but 15 cm or smaller.
• pT4 — Tumor is more than 15 cm.

Head and neck:

• pT1 — Tumor is 2 cm or smaller.
• pT2 — Tumor is more than 2 cm but 4 cm or smaller.
• pT3 — Tumor is more than 4 cm.
• pT4 — Tumor has grown into surrounding structures such as the bones of the face or skull, the eye, major blood vessels of the neck, or the brain.

Intra-abdominal and intrathoracic (within the abdomen or chest cavity):

• pT1 — Tumor is confined to one organ.
• pT2 — Tumor has grown into surrounding connective tissue of the organ of origin.
• pT3 — Tumor has grown into at least one adjacent organ.
• pT4 — Multiple tumors are present.

If no tumor is found in the resection specimen (for example, after an excellent response to pre-operative therapy), the stage is recorded as pT0. If the tumor cannot be reliably measured — for example, because the specimen was received as multiple fragments — it may be listed as pTX.

Nodal stage (pN)

• pN0 — No cancer found in any lymph nodes examined.
• pN1 — Cancer found in one or more regional lymph nodes.
• pNX — Lymph nodes were not assessed.

What is the prognosis for myxoid liposarcoma?

Compared with other liposarcoma subtypes, myxoid liposarcoma generally has a relatively favorable prognosis when low grade. However, outcomes vary considerably depending on several key factors.

The most important prognostic factor is the proportion of round cells in the tumor. Pure myxoid liposarcoma (with fewer than 5% round cells) is considered low to intermediate grade and typically behaves less aggressively, with five-year survival rates of 80–90% for localized disease. When the round cell component exceeds 5% — and particularly when it exceeds 80% — the tumor is classified as higher grade and carries a substantially worse prognosis, with a higher risk of distant metastasis.

Myxoid liposarcoma has an unusual pattern of spread compared to most other sarcomas. Rather than metastasizing primarily to the lungs, it has a well-recognized tendency to spread to unusual soft-tissue sites, including the retroperitoneum, the opposite limb, and, particularly, the spine and bones. This means that follow-up imaging must include evaluation of the whole body or skeleton in addition to the lungs. Any new back, hip, or spine pain in a patient with myxoid liposarcoma warrants prompt imaging.

Additional factors affecting prognosis include:

• Surgical margin status — Complete removal with negative margins is the strongest predictor of local control. A positive margin significantly increases the risk of tumor recurrence.
• Tumor size — Larger tumors carry a higher risk of distant spread. Most myxoid liposarcomas are large at diagnosis, which is why neoadjuvant radiation is commonly used.
• Response to neoadjuvant therapy — A good pathologic response (90% or more necrosis) after pre-operative treatment is associated with a better outcome.
• FNCLCC grade — Higher grade tumors (grade 2–3) carry a worse prognosis.
• Tumor location — Deep tumors in the thigh or retroperitoneum are generally harder to remove completely than more superficial tumors.

What happens after the diagnosis?

Treatment for myxoid liposarcoma is planned by a multidisciplinary team including a surgeon (typically an orthopedic oncologist or surgical oncologist), a radiation oncologist, and a medical oncologist. The approach depends on tumor size, location, grade, and whether the cancer has spread.

For most patients with localized disease, the standard approach is neoadjuvant radiation therapy (radiation given before surgery) followed by surgical resection — removal of the tumor with a wide margin of surrounding normal tissue. Myxoid liposarcoma is particularly sensitive to radiation, which is one reason it tends to respond well to pre-operative treatment. Surgery after radiation aims to achieve negative margins while preserving as much of the limb and its function as possible.

Chemotherapy may be added for high-grade tumors (particularly those with a significant round cell component) or for tumors at high risk of spread. Commonly used regimens include doxorubicin and ifosfamide, or trabectedin, a chemotherapy agent that has shown particular activity in myxoid liposarcoma specifically.

For locally recurrent or metastatic disease, treatment is individualized and may include additional surgery, radiation therapy, chemotherapy, or enrollment in a clinical trial. Given the unusual metastatic pattern of myxoid liposarcoma (including bony metastases), radiation therapy is sometimes used to treat metastatic deposits in the spine or other sites.

After treatment, long-term follow-up is essential. This typically includes regular MRI of the primary tumor site and imaging of the chest and whole body at intervals determined by risk. Surveillance is maintained for many years, as late recurrences can occur.

Questions to ask your doctor

Your pathology report contains important information that will guide your care. The following questions may help you prepare for your next appointment.

• What is the FNCLCC grade of my tumor, and what does that mean for my prognosis?
• What percentage of the tumor is made up of round cells, and does this affect my treatment plan?
• Was the DDIT3 gene rearrangement confirmed by FISH or NGS testing?
• How large is the tumor, and what is the pathologic stage?
• Were the surgical margins negative? If not, is further surgery or radiation being considered?
• Did my tumor extend into any surrounding structures such as muscle, bone, or blood vessels?
• Was lymphovascular or perineural invasion present?
• Were any lymph nodes examined, and did any contain tumor cells?
• If I received radiation or chemotherapy before surgery, what was the percentage of tumor necrosis — how well did the treatment work?
• Is chemotherapy recommended, given the grade and round cell component?
• What follow-up imaging will I need, and how often? Will the spine and skeleton be included, given myxoid liposarcoma’s unusual pattern of spread?
• Are there any clinical trials available for my tumor type?