Synovial sarcoma is a rare and aggressive form of cancer belonging to the group known as soft tissue sarcomas. These sarcomas originate in the body’s connective tissues, such as fat, muscle, nerves, and blood vessels. While it can affect individuals of any age, it is more frequently observed in adolescents and young adults. This malignancy accounts for a small percentage of all soft tissue tumors diagnosed annually and often presents a challenge due to its propensity for spread.
Defining Synovial Sarcoma
Synovial sarcoma is classified as a mesenchymal tumor, developing from cells that normally form connective tissue. Despite its misleading name, which suggests a connection to the synovium (the tissue lining the joints), the tumor rarely originates directly within the joint capsule itself. It is most commonly found in the deep soft tissues of the extremities, especially near large joints like the knee or ankle. The name is a historical misnomer, stemming from the tumor’s microscopic resemblance to joint lining cells when first described.
The defining characteristic of synovial sarcoma is a specific genetic alteration known as a chromosomal translocation, found in over 90% of cases. This is a rearrangement where segments of two different chromosomes break off and swap places. This involves a fusion between chromosome X and chromosome 18. Specifically, the \(SS18\) gene fuses with one of the \(SSX\) genes (typically \(SSX1\) or \(SSX2\)), creating an \(SS18:SSX\) fusion protein. This fusion gene acts as a molecular fingerprint, driving abnormal cell growth. Synovial sarcoma is considered a high-grade tumor, indicating a greater potential for rapid growth and metastasis.
Recognizing the Signs
The physical presentation of synovial sarcoma often begins subtly, contributing to delayed diagnosis. The most frequent initial sign is a mass or lump located deep within the soft tissues. This growth is usually found in the arms or legs, often situated close to a joint.
The lump is often initially painless or causes only slight tenderness, allowing it to grow large before medical attention is sought. As the mass increases in size, it may press on surrounding nerves, muscles, or blood vessels. This pressure can lead to localized pain, swelling, or a limited range of motion in the affected limb. Less common locations include the head, neck, trunk, or lungs, with symptoms varying based on the specific site.
If the tumor develops in the head or neck, symptoms may include difficulty swallowing, breathing, or changes in the voice. Because the initial symptoms can be vague, the condition is sometimes misidentified as a more common ailment, such as bursitis or a sports injury. Any persistent or growing lump in the soft tissues, especially one that is deeper than the skin layer, warrants a thorough medical evaluation.
Confirming the Diagnosis
The definitive identification of synovial sarcoma involves a sequence of imaging and tissue analysis, beginning with a physical examination and patient history. Imaging studies are the first technical step, with Magnetic Resonance Imaging (MRI) being the preferred method. MRI provides detailed pictures of the soft tissues, helping determine the exact size, depth, and extent of the mass, including its relationship to nearby structures like bone, nerves, and major blood vessels.
Computed Tomography (CT) scans are often used to evaluate the potential spread of the tumor, particularly to the lungs, a common site for metastasis. Plain X-rays may also reveal the tumor, sometimes showing characteristic calcifications within the soft tissue mass. While imaging can strongly suggest a sarcoma, it cannot provide a definitive cancer diagnosis.
The necessary step for confirmation is a biopsy, where a small sample of tumor tissue is removed for laboratory testing. This is typically performed as a core needle biopsy, often guided by imaging to ensure the sample is representative. A pathologist then examines the cells under a microscope to classify the tumor type and check for signs of malignancy.
The final and most precise diagnostic confirmation relies on molecular testing to detect the characteristic \(SS18:SSX\) fusion gene. Techniques like Fluorescence In Situ Hybridization (FISH) or Reverse Transcriptase–Polymerase Chain Reaction (RT-PCR) identify this specific genetic signature in the biopsy sample. This molecular evidence is paramount, as it accurately distinguishes synovial sarcoma from other soft tissue tumors that may appear similar under standard microscopic examination.
Overview of Treatment Options
The management of synovial sarcoma typically requires a multi-modal approach involving a team of specialists. The primary intervention is surgery, aiming to remove the entire tumor with a margin of healthy tissue surrounding it. This procedure, called wide local excision, seeks to obtain “clear margins,” meaning no cancer cells are found at the edges of the removed tissue.
Significant surgical advances have made limb-sparing procedures the standard approach for tumors in the arms and legs. Amputation is reserved for situations where the tumor has extensively involved vital structures. However, the tumor’s location near critical neurovascular bundles, such as in the popliteal fossa behind the knee, can complicate surgery and make achieving clear margins more difficult.
Radiation therapy is frequently integrated into the treatment plan, used either before or after surgery. Preoperative radiation can shrink a larger tumor, potentially making it easier to remove completely and increasing the likelihood of a successful limb-sparing operation. Postoperative radiation is delivered to the tumor bed to eliminate any microscopic cancer cells left behind, reducing the risk of local recurrence.
Chemotherapy is often considered for tumors that are large, high-grade, or have already spread to distant sites. Standard regimens often include drugs like doxorubicin and ifosfamide, which are known to be active against this sarcoma type. While its role in adult localized disease is still researched, chemotherapy is commonly recommended for younger patients and for managing metastatic disease. For advanced cases, targeted therapies, such as the drug pazopanib (which inhibits cancer cell growth signals), or enrollment in clinical trials may be considered when standard treatments are no longer effective.