Tenosynovial Giant Cell Tumors (TGCTs)
Synonyms
TGCT, pigmented villonodular synovitis , nodular tenosynovitis, giant cell tumor of the tendon sheat,Overview
Tenosynovial giant cell tumors (TGCTs) are a group of rare, typically non-life-threatening tumors that involve the synovium, bursae and tendon sheath. Synovium is the thin layer of tissue or membrane that covers the inner surface of the joint spaces and the bursae and tendon sheaths. The bursae are small fluid-filled sacs that cushion bones, tendons and muscles around the joints. A tendon sheath is a layer membrane that covers a tendon. Tendons are fibrous tissue that connects muscle to bone.
These tumors cause the affected synovium, bursae or tendon sheaths to thicken and overgrow. They are benign, which means they are not cancerous and do not spread to other areas of the body (metastasize). However, they can grow and cause damage to the surrounding tissue and structures of the affected limb. Symptoms can include pain, swelling, tenderness, warmth at the location and limitation of movement of the joint. Large or small joints can be affected depending upon the tumor subtype. In localized TGCT, smaller joints tend to be affected, such as digits and parts of the foot. In diffuse TGCT, large joints tend to be involved, most commonly the knee. Surgery is often the initial treatment option. However, depending on the subtype, the tumor can recur, particularly in diffuse TGCT which was previously known as pigmented villonodular synovitis (PVNS). If untreated or if the tumor continually recurs, they can result in damage and degeneration of the affected joint and surrounding tissues or structures. Sometimes, they can cause significant disability. In rare cases, amputation is warranted.
Symptoms
The signs and symptoms of tenosynovial giant cell tumors (TGCTs) can vary depending upon the exact location involved and the subtype present. Symptoms tend to be non-specific, and most patients report pain and swelling as a symptom of the disease. Other symptoms include limitation in range of motion, tenderness to the touch, warmth coming from the joint, clicking or popping of the joint and stiffness.
Diffuse TGCT
(also known as diffuse-type giant cell tumor; formerly, PVNS)
Diffuse TGCT usually affects a large joint; the tumor is widespread (diffuse) and affects the entire or most of the joint. TGCT is a monoarticular disease, meaning only one joint is involved. The knee is most often affected, followed by the ankle and hip. The elbow or shoulder can also be affected. In rare instances, the two joints that connect the jaw bones to the skull (temporomandibular joints) or the joints that connect vertebrae together (spinal facet joints) can be affected.
The initial symptoms are usually pain and swelling of the affected joint. Stiffness of the joint and reduction in range of motion can also occur. Usually, these symptoms have a gradual onset. There may be a feeling of warmth or tenderness on the skin of the affected joint. A painless swelling of the joint is sometimes the first sign. Sometimes, swelling can be significant. Affected individuals may have a sensation of the affected joint ‘locking’ or ‘catching.’ There may be a popping sound on occasion and the joint may feel unstable. Symptoms can occur suddenly and intermittently and are often referred to as a “flare”.
Diffuse TGCT can progress to cause arthritic damage and degeneration to the joint and damage to the surrounding cartilage and bone. If untreated, diffuse TGCT can potentially cause chronic, debilitating disease and significant functional impairment of the affected joint. Surgery is the main form of initial treatment, but the disease often recurs. With the discovery of drug options, the initial treatment may not always be surgery if the disease cannot be removed in its entirety. More often, drug options are used following recurrence or when patients have high risk of recurrence or morbidity (complications or consequences) from surgery. In asymptomatic patients, an active surveillance approach may be taken due to the high recurrence rate. Active surveillance includes MRIs to monitor disease and evaluation of symptoms.
Localized TGCT
(Intraarticular GCTTS, formerly localized PVNS; extraarticular GCTTS; formerly nodular tenosynovitis)
Localized TGCT usually presents as a growth or mass of abnormal tissue (nodules) or as a small growth that is connected to the affected area with a stalk of abnormal tissue (pedunculated mass). These tumors are usually limited to a specific area of the joint (localized), are well-defined (encapsulated) and typically affect smaller joints such as those of the hands and toes. However, localized TGCT can impact other joints such as the knee. The initial sign is often a swelling. The tumor grows slowly over time. Sometimes they cause pain. Eventually, affected individuals may have a sensation of the affected joint ‘locking’ or ‘catching.’ The affected joint may become unstable. Unlike the diffuse form, these tumors are unlikely to cause destructive changes to the joint or surrounding areas and are less likely to recur after treatment. Surgery is the main form of treatment and is often curative.
Causes
A minority of the cells that make up a TGCT (2-16%) carry a specific chromosomal translocation. Chromosomes, which are present in the nucleus of all human cells, carry genetic information for each individual, like the blueprint of the body. Each human body cell normally has 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated “p” and a long arm designated “q”. Chromosomes are further sub-divided into many bands that are numbered. For example, “chromosome 11p13” refers to band 13 on the short arm of chromosome 11. The numbered bands specify the location of the thousands of genes that are present on each chromosome.
A chromosomal translocation is when a piece or region of certain chromosomes break off and are rearranged, resulting in shifting of genes and an altered set of chromosomes. In these tumors, there is a translocation involving specific regions on chromosome 1 and chromosome 2. This is written as [t (1;2) (p13;q37)]. Cells containing this translocation overproduce a type of protein called colony stimulating factor-1 or CSF-1. These cells only make up a small portion of the cells in the tumor. However, because they overproduce CSF-1, they attract other cells in the body, specifically cells that have a CSF-1 receptor. A receptor is a protein molecule on the surface of the cell that receives chemical signals from outside the cell. CSF-1 binds to a CSF-1 receptor, like a baseball to a glove. Cells that have CSF-1 receptors include a type of white blood cell called macrophages and several other cells. It is these other cells that make up the bulk of a tenosynovial giant cell tumor. The TGCT cells use CSF-1 to recruit the white blood cells to incorporate into the tumor. These other cells most likely cause the inflammatory changes that are associated with these tumors.
It is not known what causes the translocation involving chromosomes 1 and 2. It may occur randomly, for no apparent reason. There are no environmental, genetic, occupational, lifestyle, demographic or regional risk factors that have been conclusively shown to be involved with the development of these tumors.
Diagnosis
A diagnosis of TGCT is based upon identification of characteristic symptoms, a detailed patient history, a thorough clinical evaluation and a variety of specialized tests. The initial symptoms of these tumors are often vague and may go unrecognized. Consequently, there is usually a significant delay, 3-4 years on average, from the onset of symptoms until a diagnosis is made.
Clinical Testing and Workup
X-rays can help with a diagnosis of the damage resulting from the tumors. Plain x-rays, called radiographs, can help to rule out other conditions and can sometimes show damage or degeneration to the surrounding bone or cartilage. X-rays will not be effective in helping to diagnose all patients with these tumors, especially if the tumors have not caused damage to surrounding bone or cartilage. X-rays may be useful to rule out other diseases but do not establish a diagnosis of TGCT. A specialized imaging technique called magnetic resonance imaging, or MRI, is the most frequently used and this examination can be very effective in helping to diagnose these tumors. MRI is the preferred technique for the detection and characterization of TGCT. An MRI uses a magnetic field and radio waves to produce cross-sectional images of certain organs and bodily tissues. MRI can be used with and without a contrasting dye, allowing the radiologist more insight into blood vessels and other vasculature specific to the joint and tumor growth. An MRI can reveal distinctive changes that indicate a tenosynovial giant cell tumor, such as hemosiderin (iron-containing compound that stains the tumors a rusty color) deposits that become apparent on MRI.
Sometimes, doctors will take a sample of synovial fluid; this is a viscous fluid found in synovial joints that reduces friction between cartilage of the joint during movement. With TGCTs, synovial fluid is often bloody and will indicate a need for further testing. Sometimes, surgical removal and microscopic examination of affected tissue (biopsy), may be necessary to confirm a diagnosis. A biopsy allows doctors to see what kind of cells make up a tumor. However, many patients are diagnosed with MRI alone due to advancements in imaging resolution.
It is important to differentiate between diffuse TGCT and localized TGCT as the prognosis and treatment of these conditions can be different. There is no microscopic difference between the features of these two subtypes, however, through imaging, cell behavioral changes can be identified. Imaging is the sole way the cell behavior and subtype is established.
Treatment
Surgery is often the initial treatment option. However, there is no current consensus on the standard of care or the optimal surgical technique. Surgery for localized TGCT tends to be curative. However, there is a risk of recurrence around 10-15%. Diffuse TGCT tends to slowly get worse (progressive disease) and often recurs after surgery at a higher rate around 50-70%. Following the first recurrence, subsequent recurrence rate can be as high as 88%. It has been shown in a single nationwide study that patients initially treated at an expert cancer center have lower recurrence rates (42%) compared to patients initially treated at community centers (92%). Therefore, patients should be seen at multidisciplinary expert centers when possible.
The specific surgical techniques a surgeon will use depend on several factors including the location and extent of the disease. TGCT is typically treated with synovectomy, removing the involved area of the lining. There is no consensus on the optimal synovectomy technique, whether arthroscopic or open surgery. Synovectomy involves the complete removal of the affected synovium (the membrane lining the inside of a joint). Completely removing the diseased synovium may not always be possible. During open surgery, a surgeon will create an incision (large opening) that allows them full access to the affected joint. This will allow the surgeon to remove the diseased tissue. Arthroscopic surgery involves creating a much smaller incision through which very small instruments are placed. These instruments include a tiny camera that allows the surgeon to see within the diseased joint and surgically remove the diseased tissue.
There have not been formal randomized studies comparing open surgery versus arthroscopic surgery. According to reports in the medical literature, some physicians have had better experiences with open surgery, while others have had better results with arthroscopic surgery. This is based on surgeon’s preference. Sometimes, a combination of arthroscopic and open surgery may be used, especially in the knee. In severe, resistant cases, total joint replacement has been tried to repair the extensive damage to the bone. However, the replacement does not address the tumor itself and is used in combination with a synovectomy to address the tumors and improve joint health. Joint replacements have similar recurrence rates as open surgeries.
The surgical removal of part of the disease, and not the entirety of it, is known as debulk surgery. The adequacy of this approach is controversial as symptoms may not be correlated to the extent of disease.
Historically, radiation therapy has been used as an adjunct treatment to surgery, particularly in cases where there is incomplete removal (resection) of the tumor. An adjunct therapy is one that is used alongside the main (or primary) therapy. There are two types of radiation, external beam radiation and intraarticular radiation, or isotopic synoviorthesis. Intraarticular radiation therapy alone (radiation therapy as a primary treatment) has also been attempted but has had inconclusive and variable results. Information on radiation therapy as a primary or adjuvant therapy is limited to small, poor-quality, single institution reports and, therefore, has not yet been conclusively established. Additionally, there is a risk of secondary radiation-induced sarcoma. Due to this risk and the lack of established efficacy, radiation treatment is not recommended and should not be used to substitute suboptimal treatment.
In 2019, a medicine that targets the disease, specifically CSF-1, was approved. Pexidartinib (Turalio), the first CSF-1 inhibitor, was approved by the U.S. Food and Drug Administration (FDA) for the treatment of adult patients with symptomatic tenosynovial giant cell tumor associated with severe disease or functional limitations and not amenable to improvement with surgery. Turalio showed over 50% response in TGCT patients, 39% of TGCT patients having partial response and 18% having complete response.
Imatinib (Gleevec) and nilotinib (Tasigna) are often used off-label to treat TGCT. Imatinib has shown that 33% of patients have a significant reduction in tumor size, with 27% having partial shrinkage and 4% having unmeasurable disease. Other medicines are now being investigated for their inhibition of CSF-1 and tumor shrinkage.