Liposarcomas are a rare form of cancer originating in fat cells. This soft tissue sarcoma is most frequently found in the deep soft tissues of the limbs, such as the thigh, or within the abdomen (retroperitoneum). Liposarcomas are malignant tumors that can invade surrounding tissues and spread to distant sites. The initial sign is often a painless, growing lump.
Liposarcoma Subtypes Determine Behavior
Whether a liposarcoma grows quickly depends entirely on its specific cellular subtype. Liposarcomas are a group of tumors classified into distinct types based on their cellular appearance and genetic makeup. The World Health Organization classifies liposarcoma into four main categories, each with a different biological behavior.
The most common subtype, accounting for up to 50% of cases, is Well-Differentiated Liposarcoma (WDLPS). This type is considered low-grade and is often characterized by slow, localized growth. WDLPS can sometimes progress into a more aggressive form known as Dedifferentiated Liposarcoma (DDLPS).
Dedifferentiated Liposarcoma is a high-grade tumor associated with a more aggressive clinical course. Myxoid Liposarcoma (MLS) is the second most common subtype and is sometimes grouped with its high-grade variant, Round Cell Liposarcoma (RCLS), into Myxoid/Round Cell Liposarcoma (MRCLS). Pleomorphic Liposarcoma (PLPS) is the rarest form, making up less than 10% of cases, and is highly aggressive from the outset.
Understanding the Speed of Tumor Growth
The speed of growth varies dramatically across the liposarcoma spectrum. Well-Differentiated Liposarcoma is indolent, often remaining stable or growing very slowly over years. This low-grade nature means it rarely metastasizes to other organs, though it has a high propensity for local recurrence after treatment.
Dedifferentiated Liposarcoma is characterized by rapid, aggressive growth. This high-grade tumor invades surrounding tissues quickly and has a significant risk of distant metastasis, with spread occurring in 15% to 30% of cases.
Pleomorphic Liposarcoma is also a highly aggressive, fast-growing tumor, frequently presenting as a rapidly enlarging mass. Patients often report the mass growing noticeably over just a few months. This subtype has a high metastatic rate, with spread most commonly occurring to the lungs.
Myxoid Liposarcoma generally has an intermediate growth rate, but its behavior is heavily influenced by the presence of round cells. Tumors with a higher percentage of the round cell component are more aggressive and grow much faster. A unique characteristic of MRCLS is its tendency to metastasize to unusual extrapulmonary sites, such as the bone and other soft tissues, even when the primary tumor is small.
Identifying and Classifying the Tumor
Determining the tumor’s subtype and potential growth speed requires a precise diagnostic sequence. Initial detection involves a physical examination of a painless mass, followed by specialized imaging. Magnetic Resonance Imaging (MRI) is the preferred method, providing detailed images of the tumor’s size, location, and relationship to nearby structures like nerves and blood vessels.
Computed Tomography (CT) scans may also be used to assess the tumor’s extent, especially in the abdomen, and to check for potential spread. Imaging alone is not sufficient for definitive diagnosis. The only way to confirm malignancy and determine the specific subtype is through a core needle biopsy.
During a biopsy, a tissue sample is removed and examined by a pathologist for cellular features and genetic markers. This analysis determines the tumor’s grade and subtype, which informs the likely growth speed and the patient’s prognosis. Accurate classification is foundational for planning effective treatment, especially differentiating slow-growing WDLPS from faster-growing subtypes.
Treatment and Long-Term Monitoring
The clinical response to a liposarcoma is tailored to its identified subtype and growth characteristics. Surgical resection, which involves removing the tumor with a surrounding margin of healthy tissue (wide excision), remains the primary treatment for all liposarcomas. The goal is complete surgical removal to minimize the risk of local recurrence.
Adjuvant therapies, such as radiation or chemotherapy, are frequently employed for faster-growing, high-grade subtypes like DDLPS and PLPS. Radiation therapy can be used before or after surgery to improve local control and reduce recurrence, especially for larger tumors. Chemotherapy is often reserved for the most aggressive tumors or those that have already spread, as its effectiveness varies significantly by subtype.
Myxoid Liposarcoma is relatively sensitive to chemotherapy, particularly agents like trabectedin, used to treat unresectable or metastatic disease. Long-term monitoring is crucial for all patients due to the risk of local recurrence, which is particularly high for DDLPS and retroperitoneal WDLPS. Surveillance involves frequent follow-up appointments and imaging scans to detect any potential regrowth early.