Well-differentiated liposarcoma is a type of cancer that originates from the body’s fat cells. This condition is considered a soft tissue sarcoma, a rare group of cancers that form in the soft tissues connecting, supporting, and surrounding other body structures. Well-differentiated liposarcoma is known for its slow-growing nature, accounting for approximately 40% to 45% of all liposarcoma diagnoses.
Understanding Well Differentiated Liposarcoma
The term “well differentiated” indicates that the cancerous cells closely resemble normal, mature fat cells when viewed under a microscope. This characteristic suggests less aggressive behavior, as these tumors rarely spread to distant parts of the body. Despite their resemblance to normal fat, these cancer cells exhibit abnormal shapes and sizes, along with at least some nuclear atypia. Well-differentiated liposarcoma is considered a low-grade sarcoma.
These tumors can arise in various locations throughout the body where fat tissue is present. Common sites include the retroperitoneum and the limbs. Other less frequent locations include the mediastinum and the paratesticular area. The presence of genetic changes, particularly the amplification of the 12q13-15 chromosomal region, is a hallmark of well-differentiated liposarcoma, occurring in about 90% of cases. This amplification can lead to the overexpression of genes like MDM2 and CDK4, which play a role in promoting uncontrolled cell growth.
Diagnosing Well Differentiated Liposarcoma
The diagnostic process for well-differentiated liposarcoma begins with imaging techniques to visualize the tumor and assess its characteristics. Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) scans are used to evaluate the tumor’s size, location, and its relationship to surrounding tissues. On imaging, these tumors often appear predominantly fatty but may also show thick septa, nodular soft-tissue components, or areas of prominent enhancement after contrast administration, which can help distinguish them from benign fatty tumors.
A definitive diagnosis relies on a biopsy, which can be either a core needle biopsy or an incisional biopsy. Pathologists examine tissue samples under a microscope to identify the characteristic features of well-differentiated liposarcoma, such as mature adipocytes with variations in cell size and nuclear atypia. Distinguishing well-differentiated liposarcoma from benign fatty tumors, or lipomas, is a primary challenge for pathologists, as their microscopic appearances can be very similar.
Specialized tests, such as immunohistochemistry for MDM2 and CDK4 protein expression or fluorescence in situ hybridization (FISH) for MDM2 gene amplification, are used to confirm the diagnosis and differentiate it from benign lipomas. While core needle biopsies have a high overall diagnostic accuracy for adipocytic tumors, their accuracy for well-differentiated liposarcomas, distinguishing them from benign lipomas, is around 81%. This is partly because these tumors can be heterogeneous, meaning different areas within the same tumor may show varying characteristics, and a biopsy might miss a more aggressive component.
Treatment for Well Differentiated Liposarcoma
Surgical excision is the primary treatment for well-differentiated liposarcoma. The goal of surgery is to achieve complete removal of the tumor along with a margin of healthy surrounding tissue. This approach helps to minimize the risk of local recurrence. For tumors located in the extremities, complete surgical removal is achievable.
However, in more complex anatomical regions like the retroperitoneum, achieving clear surgical margins can be challenging due to the proximity of vital organs. In such cases, the tumor may be very large by the time it is diagnosed, making complete removal more difficult. Despite successful initial surgery, local recurrence rates for well-differentiated liposarcomas, especially in the retroperitoneum, range from 30% to 60% within five years.
Radiation therapy is considered in conjunction with surgery, particularly when complete surgical removal is difficult or for local disease control. For retroperitoneal tumors, radiation therapy is given before surgery to limit toxicity to surrounding organs. Chemotherapy has a limited role in the treatment of well-differentiated liposarcoma because these slow-growing tumors show low sensitivity to conventional chemotherapy agents. Chemotherapy is not used as a first-line treatment, but may be considered for unresectable or metastatic forms of liposarcoma.
Long-Term Outlook and Monitoring
The long-term outlook for individuals with well-differentiated liposarcoma is favorable, especially when the tumor is located in an extremity and can be completely removed. While these tumors are considered low-grade and rarely metastasize, local recurrence remains a concern if the tumor is not entirely excised. The risk of local recurrence is particularly higher for tumors in the retroperitoneum.
Ongoing surveillance is therefore an important aspect of post-treatment care. Regular imaging, such as MRI or CT scans, is performed to detect any signs of recurrence early. The frequency of these follow-up scans depends on the tumor’s initial location and other factors.
A rare but concern is the possibility of dedifferentiation, where the well-differentiated tumor transforms into a more aggressive form of liposarcoma. This transformation is associated with an increased risk of local recurrence and a higher potential for metastasis. Dedifferentiation can occur years after the initial diagnosis, highlighting the importance of consistent long-term monitoring to identify any changes in tumor behavior promptly.