Dedifferentiated Liposarcoma: Understanding Your Pathology Report

by Bibianna Purgina, MD FRCPC
April 12, 2026

Dedifferentiated liposarcoma is an aggressive type of sarcoma — a cancer that arises from fat cells. It is called dedifferentiated because it develops from within a less aggressive fatty tumor called well-differentiated liposarcoma (also known as atypical lipomatous tumor). During this transformation, a portion of the tumor’s fat cells are replaced by a completely different type of high-grade cancer cell that no longer resembles fat at all. The result is a tumor that contains two distinct areas: a well-differentiated fatty component and a high-grade non-fatty component. It is the high-grade component that makes dedifferentiated liposarcoma significantly more dangerous than its precursor. Dedifferentiated liposarcoma most commonly arises in the retroperitoneum — the space at the back of the abdominal cavity — and less commonly in the arms, legs, or trunk. It primarily affects adults in their fifth through seventh decades of life. Other liposarcoma subtypes include myxoid liposarcoma and pleomorphic liposarcoma.

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 dedifferentiated liposarcoma?

Dedifferentiated liposarcoma is caused by a specific genetic change: amplification of the MDM2 gene and, in most cases, the CDK4 gene as well. Amplification means that the tumor cells contain many more copies of these genes than normal cells do. MDM2 normally helps regulate a protein called p53, which acts as a brake on cell growth. When MDM2 is amplified, this braking system is disrupted, allowing fat cells to grow and divide uncontrolled — and eventually dedifferentiate into a more aggressive cancer cell type. During dedifferentiation, tumor cells acquire additional genetic changes beyond MDM2/CDK4 amplification, driving the shift toward high-grade behavior. This genetic change is not inherited and does not typically run in families. The exact reason why MDM2 amplification and subsequent dedifferentiation occur is not fully understood.

What are the symptoms?

Dedifferentiated liposarcoma most often presents as a large, painless mass. Tumors in the retroperitoneum — the deep abdominal space behind the organs — can grow very large before causing symptoms, because this location provides little resistance to tumor growth. By the time a retroperitoneal tumor is discovered, it may measure 20 cm or more. Symptoms that may occur include abdominal fullness or discomfort, a visible or palpable abdominal mass, or compression of nearby structures such as the kidney, ureter, or large blood vessels. Tumors arising in the arms or legs typically present as a firm, deep lump that may increase in size. In some cases, the tumor is discovered incidentally when imaging is performed for an unrelated reason.

How is the diagnosis made?

The diagnosis of dedifferentiated liposarcoma is made by examining a tissue sample under the microscope. The sample is usually obtained through a biopsy — most often a core needle biopsy performed under imaging guidance, in which a needle is passed into the tumor to collect small cylinders of tissue. In some cases, the diagnosis is made after the entire tumor is surgically removed. The tissue is sent to a pathologist, who examines it under the microscope.

Under the microscope, dedifferentiated liposarcoma has two distinct components. The first is a well-differentiated component made up of abnormal fat cells that still resemble normal fat — this is the precursor well-differentiated liposarcoma from which the tumor arose. The second is a dedifferentiated component made up of high-grade cancer cells that no longer resemble fat at all. These high-grade cells often resemble those of other aggressive sarcomas, such as undifferentiated pleomorphic sarcoma, myxofibrosarcoma, or osteosarcoma. It is the combination of a well-differentiated fatty area alongside a high-grade non-fatty sarcoma that allows pathologists to make the diagnosis. To confirm the diagnosis and distinguish dedifferentiated liposarcoma from other tumors that can look similar, pathologists use a test called fluorescence in situ hybridization (FISH) to detect MDM2 gene amplification. Finding more MDM2 copies than normal confirms the diagnosis. Once confirmed, imaging — typically CT or MRI — is used to assess the full extent of the disease and determine whether it has spread to other organs.

Histologic grade

Pathologists use the FNCLCC grading system (developed by the French Federation of Cancer Centers Sarcoma Group) to grade dedifferentiated liposarcoma. This system scores three microscopic features of the dedifferentiated (high-grade) component of the tumor and adds the scores together to produce a final grade. The grade reflects how aggressive the high-grade component is likely to behave.

Because dedifferentiated liposarcoma cells look nothing like normal fat cells, they always receive the maximum differentiation score (3 points). As a result, the overall FNCLCC score is always at least 5 points, placing all dedifferentiated liposarcomas at grade 2 or grade 3 — never grade 1. In practice, most dedifferentiated liposarcomas are grade 2 or grade 3 high-grade tumors.

• Tumor differentiation — Describes how closely the tumor cells resemble normal fat cells. Because the dedifferentiated cells look very different from fat, they always receive 3 points. This score is fixed for dedifferentiated liposarcoma.
• Mitotic count — Counts the number of actively dividing cells (called mitotic figures) seen in ten microscopic fields. Tumors with 0–9 mitotic figures per 10 fields receive 1 point; those with 10–19 mitotic figures per 10 fields receive 2 points; those with 20 or more mitotic figures per 10 fields receive 3 points. Higher mitotic counts indicate faster tumor growth.
• Necrosis — Necrosis is a form of cell death appearing as areas of dead tissue within the tumor. No necrosis scores 0 points; necrosis in less than half the tumor scores 1 point; necrosis in half or more of the tumor scores 2 points.

The final grades are:

• Grade 1 — Total score of 2 or 3. Not applicable for dedifferentiated liposarcoma.
• Grade 2 — Total score of 4 or 5. Intermediate-grade; moderately aggressive.
• Grade 3 — Total score of 6 to 8. High-grade; more aggressive, faster-growing, and more likely to spread than grade 2.

Tumor size

The tumor is measured in three dimensions, but only the largest single measurement is typically recorded in your pathology report as the tumor size. Tumor size is used to determine the pathologic tumor stage (pT). Tumors 5 cm or smaller are generally associated with a better prognosis than larger tumors. The final tumor size is measured from the surgically removed specimen. Retroperitoneal dedifferentiated liposarcomas are frequently very large at diagnosis — often 15–30 cm — because of the available space in the abdominal cavity and the absence of early symptoms.

Tumor extension

Dedifferentiated liposarcoma typically arises within a fat-containing compartment of the body but can invade adjacent structures as it enlarges. This spread beyond the original site is called tumor extension. The pathologist carefully examines all tissue submitted with the resection specimen to determine whether tumor cells have grown into surrounding muscles, organs, nerves, or blood vessels. In retroperitoneal tumors, the kidney, adrenal gland, colon, small bowel, and major blood vessels may be involved. Extension into surrounding structures increases the pathologic tumor stage (pT) and may affect whether complete surgical removal is achievable.

Treatment effect

Some patients with dedifferentiated liposarcoma receive chemotherapy and/or radiation therapy before surgery. This is called neoadjuvant therapy, and its purpose is to shrink the tumor before removal. After surgery, the pathologist examines the removed tissue and estimates the proportion of the tumor that is non-viable (dead) versus viable (still alive). A tumor that is 90% or more non-viable indicates an excellent response to pre-operative therapy and is associated with a better outcome. When a significant proportion of viable tumor remains, additional treatment after surgery may be considered. Your report will describe the estimated percentage of viable and non-viable tumor.

Lymphovascular invasion

Lymphovascular invasion (LVI) means that tumor cells were found inside the thin-walled channels of blood vessels or lymphatic vessels within or near the tumor. Lymphatic vessels connect to lymph nodes and carry a fluid called lymph throughout the body; blood vessels carry blood. When tumor cells enter these channels, they can travel to lymph nodes or distant organs. The presence of LVI is reported as present or absent in your pathology report and is an adverse finding that increases the risk of spread.

Perineural invasion

Perineural invasion means that tumor cells were found attached to or growing along a nerve. Nerves run throughout the body and carry signals between the body and the brain. When cancer cells grow along a nerve, they can spread into adjacent tissues beyond what is visible at the time of surgery, increasing the risk of local recurrence. Perineural invasion is reported as present or absent and may influence decisions about the extent of surgery or the use of radiation therapy.

Surgical margins

In pathology, a margin is the edge of tissue removed during surgery. Margin status indicates whether the entire tumor was removed or whether cancer cells remain at the cut edge of the tissue. Achieving clear (negative) surgical margins is one of the most important goals of surgery and is a key predictor of local control.

• Negative margin — No tumor cells are present at the cut edge. This suggests the tumor was completely removed. The distance from the nearest tumor cells to the margin may also be recorded, as a wider clear margin is associated with a lower risk of local recurrence.
• Close margin — Tumor cells are very close to the cut edge but do not reach it. This may increase the risk of local recurrence and may prompt further treatment planning.
• Positive margin — Tumor cells are present at the cut edge, meaning some cancer may remain in the body. Additional surgery or radiation therapy is commonly recommended.

Achieving clear margins in retroperitoneal dedifferentiated liposarcoma is particularly challenging because the tumor is often very large, intimately associated with vital structures, and not surrounded by a well-defined capsule. This difficulty is a major contributor to the high local recurrence rates seen in retroperitoneal disease.

Lymph nodes

Spread of dedifferentiated liposarcoma to lymph nodes is uncommon but more likely than with well-differentiated liposarcoma or ALT alone, reflecting the higher-grade biology of the dedifferentiated component. Lymph nodes are not routinely removed during surgery unless they are visibly enlarged or clinically suspicious. If lymph nodes were removed, the pathologist will examine them under the microscope and report the number of nodes examined, the number containing tumor cells, and whether extranodal extension — spread of tumor cells through the outer capsule of the lymph node into surrounding tissue — is present. Finding tumor cells in a lymph node is an adverse finding and increases concern for distant spread.

Biomarker and molecular testing

Molecular testing plays an important role in both diagnosing dedifferentiated liposarcoma and — increasingly — in guiding treatment decisions for patients with advanced or recurrent disease.

MDM2 and CDK4 amplification

Amplification of the MDM2 and CDK4 genes is the defining molecular feature of dedifferentiated liposarcoma and is confirmed using FISH testing. Both genes play a role in controlling cell growth: MDM2 suppresses the p53 tumor-suppressor protein, and CDK4 drives the cell cycle forward. When both are amplified, the normal controls on cell growth are lost. Beyond confirming the diagnosis, these genes are active targets of ongoing drug development. MDM2 inhibitor drugs — designed to restore p53 function by blocking the MDM2 protein — are being investigated in clinical trials for well-differentiated and dedifferentiated liposarcoma. CDK4 inhibitors, which are already approved for use in breast cancer, are also under study in liposarcoma. If your tumor has recurred or progressed, your oncologist may discuss whether a clinical trial targeting MDM2 or CDK4 is appropriate.

Next-generation sequencing (NGS)

In patients with recurrent, locally advanced, or metastatic dedifferentiated liposarcoma, comprehensive molecular profiling using next-generation sequencing (NGS) may be performed to look for additional genetic changes beyond MDM2/CDK4 amplification. These additional changes — which may include mutations in genes such as TP53, RB1, ATRX, and others — can vary across tumors and may help determine eligibility for a clinical trial or targeted therapy. NGS is not routinely performed on all dedifferentiated liposarcomas at the time of first diagnosis, but it becomes increasingly relevant in the setting of recurrent or treatment-resistant disease. Your oncologist will advise whether molecular profiling is appropriate in your situation.

For more information about biomarkers and molecular testing in cancer, visit the Biomarkers and Molecular Testing section of this website.

Pathologic stage (pTNM)

The pathologic stage for dedifferentiated liposarcoma is based on the TNM staging system developed by the American Joint Committee on Cancer (AJCC), 8th edition. This system uses information about the primary tumor (T), lymph nodes (N), and distant metastatic disease (M) to describe the extent of cancer. The M stage — whether the cancer has spread to distant organs such as the lungs — is determined by imaging, not by the pathology report. In general, a higher stage reflects more advanced disease and a less favorable prognosis. Because dedifferentiated liposarcoma can arise in many body sites, the tumor (pT) staging criteria vary depending on where the tumor started.

Tumor stage (pT)

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.

Trunk and extremities (chest wall, back, abdomen, arms, and legs):

• 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.

Thoracic visceral organs (organs inside the chest):

• pT1 — Tumor is confined to one organ.
• pT2 — Tumor has grown into the connective tissue immediately surrounding the organ where it started.
• pT3 — Tumor has grown into at least one adjacent organ.
• pT4 — Multiple separate tumors are present.

Retroperitoneum (the space at the back of the abdominal cavity):

• 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.

Orbit (the bony socket surrounding the eye):

• pT1 — Tumor is 2 cm or smaller.
• pT2 — Tumor is more than 2 cm but has not grown into the bones surrounding the eye.
• pT3 — Tumor has grown into the bones surrounding the eye or other bones of the skull.
• pT4 — Tumor has grown into the eye itself or surrounding structures including the eyelids, sinuses, or brain.

• pT0 — No viable tumor found in the resection specimen. This may occur after a complete response to neoadjuvant therapy.
• pTX — The tumor cannot be reliably assessed, for example because the specimen was received as multiple small fragments.

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?

Dedifferentiated liposarcoma is significantly more aggressive than its precursor, well-differentiated liposarcoma or ALT. The prognosis depends primarily on tumor location, stage at diagnosis, margin status, and FNCLCC grade.

Overall five-year survival rates for dedifferentiated liposarcoma range from approximately 40–60% across all stages and sites, but outcomes differ substantially by location:

• Extremity dedifferentiated liposarcoma — Tumors in the arms or legs are typically discovered at a smaller size and are more likely to be completely resected. Five-year survival rates for extremity disease are generally better than for retroperitoneal disease, approaching 60–70% when complete resection is achieved.
• Retroperitoneal dedifferentiated liposarcoma — This is the more common and more challenging presentation. Tumors are often very large at diagnosis, negative margins are difficult to achieve, and local recurrence is common after surgery. Five-year overall survival for retroperitoneal disease is approximately 40–55%, with local recurrence as the dominant pattern of failure. Distant metastases — most commonly to the lungs and liver — occur in approximately 15–30% of patients.

The following features are associated with a worse outcome:

• Positive or close surgical margins — The most important predictor of local recurrence. Wide negative margins are the primary goal of surgery.
• Higher FNCLCC grade — Grade 3 tumors are more aggressive, faster-growing, and more likely to spread to distant organs than grade 2 tumors.
• Large tumor size — Tumors greater than 5 cm — and especially those greater than 10 or 15 cm — are associated with worse outcomes. Most retroperitoneal tumors fall into these larger size categories at diagnosis.
• Retroperitoneal location — Associated with higher recurrence rates and lower likelihood of complete resection compared with extremity disease.
• Distant metastasis — Patients with metastatic disease at presentation have significantly worse outcomes. Median survival with metastatic dedifferentiated liposarcoma is typically less than 18 months with current treatments.
• Presence of necrosis — Extensive tumor necrosis (contributing to a higher FNCLCC score) is associated with more aggressive behavior.

What happens after the diagnosis?

After the diagnosis is confirmed, care is best managed by a multidisciplinary team that includes a surgical oncologist, a medical oncologist with expertise in sarcoma, and a radiation oncologist. Referral to a sarcoma center with experience in retroperitoneal and high-grade soft tissue tumors is strongly recommended, particularly for large or retroperitoneal tumors. These centers offer access to specialized surgical expertise, clinical trials, and multidisciplinary decision-making.

Surgery is the cornerstone of treatment for localized dedifferentiated liposarcoma. The goal is complete removal of the tumor with negative margins. For retroperitoneal tumors, this often requires removal of adjacent organs — such as a kidney, adrenal gland, or segment of colon — as part of a planned en bloc resection to achieve the widest possible margins. This approach, used at specialized sarcoma centers, is associated with improved local control.

Radiation therapy may be used before or after surgery to reduce the risk of local recurrence. For retroperitoneal tumors, preoperative radiation is increasingly used at high-volume centers and may allow a safer and more complete resection. For extremity tumors with close or positive margins, postoperative radiation is routinely offered. The role of radiation is individualized based on tumor size, location, and margin status.

Chemotherapy is used for locally advanced, unresectable, or metastatic dedifferentiated liposarcoma, and may also be considered as neoadjuvant (pre-operative) therapy for selected high-grade or borderline resectable tumors. The most commonly used first-line regimens include doxorubicin alone or combined with ifosfamide. Gemcitabine combined with docetaxel is an option in later lines of therapy. Dedifferentiated liposarcoma is generally less chemosensitive than some other high-grade sarcomas, and response rates to standard chemotherapy are modest.

Targeted therapy and clinical trials are particularly important for dedifferentiated liposarcoma. Because MDM2 and CDK4 amplification are essentially universal in this tumor, drugs that target these proteins are under active investigation. MDM2 inhibitors and CDK4 inhibitors have shown promising activity in early clinical trials. Participation in a clinical trial is strongly encouraged for patients with recurrent, unresectable, or metastatic disease and should be discussed with your oncologist at any specialized sarcoma center.

Surveillance after treatment includes regular physical examination and cross-sectional imaging of the primary site and the chest (CT or MRI) to monitor for local recurrence and lung metastases. Because local recurrence is the dominant pattern of failure — especially in retroperitoneal disease — follow-up imaging of the abdomen and pelvis is a standard part of surveillance. Recurrent disease can sometimes be treated with repeat surgery, and early detection gives patients the best chance of re-resection with clear margins. The frequency and duration of surveillance will be determined by your treatment team based on your specific situation.

Questions to ask your doctor

• Where exactly did the dedifferentiated liposarcoma arise, and how large was the tumor at the time of surgery?
• What is the FNCLCC grade of my tumor, and what does that mean for how aggressively it is likely to behave?
• Were the surgical margins clear, and how close was the tumor to the cut edge of the tissue?
• What proportion of the tumor was the dedifferentiated (high-grade) component, and what did it look like under the microscope?
• Was MDM2 amplification testing (FISH) performed to confirm the diagnosis?
• Was lymphovascular or perineural invasion identified in my tumor?
• Was any spread to lymph nodes found?
• What is the pathologic stage of my tumor?
• Will I need radiation therapy, chemotherapy, or additional surgery based on these results?
• What imaging will be used to monitor for local recurrence and distant spread, and how often will I be scanned?
• Should molecular profiling (next-generation sequencing) be performed on my tumor?
• Are there clinical trials I should consider, particularly for MDM2 or CDK4 inhibitors?
• Should I be seen at a sarcoma specialty center, and would a second pathology opinion be helpful?