Tenosynovial giant cell tumor (TGCT) is a group of rare tumors that form in the joints. TGCT is not typically cancerous, but it can grow and damage surrounding structures.

These tumors grow in three areas of the joint:

  • synovium: the thin layer of tissue that lines the inner joint surfaces
  • bursae: fluid-filled sacs that cushion tendons and muscles around the joint to prevent friction
  • tendon sheath: a layer of tissue around tendons

TGCTs are divided into types based on where they are and how quickly they grow. Localized giant cell tumors grow slowly. They start in smaller joints like the hand. These tumors are called giant cell tumors of the tendon sheath (GCTTS).

Diffuse giant cell tumors grow quickly and affect large joints like the knee, hip, ankle, shoulder, or elbow. These tumors are called pigmented villonodular synovitis (PVNS).

Both localized and diffuse TGCTs are found inside the joint (intra-articular). Diffuse giant cell tumors can also be found outside the joint (extra-articular). In rare cases, they can spread to sites like the lymph nodes or lungs.

TGCTs are caused by a change to a chromosome, called a translocation. Pieces of a chromosome break off and change places. It isn’t clear what causes these translocations.

Chromosomes contain the genetic code for producing proteins. The translocation leads to the excess production of a protein called colony-stimulating factor 1 (CSF1).

This protein attracts cells that have CSF1 receptors on their surface, including white blood cells called macrophages. These cells clump together until they eventually form a tumor.

TGCTs often start in people who are in their 30s and 40s. The diffuse type is more common in men. These tumors are extremely rare — only 11 out of every 1 million people in the United States are diagnosed each year.

Which specific symptoms you get depend on the type of TGCT you have. Some common symptoms of these tumors include:

  • swelling or a lump in the joint
  • stiffness in the joint
  • pain or tenderness in the joint
  • warmth of the skin over the joint
  • a locking, popping, or catching sound when you move the joint

Your doctor may be able to diagnose TGCT based on a description of your symptoms and a physical exam. These tests can help with the diagnosis:

  • X-ray
  • magnetic resonance imaging (MRI)
  • synovial fluid sample from around the joints
  • biopsy of tissue from the joint

Doctors usually treat TGCT with surgery to remove the tumor, and sometimes to remove part or all of the synovium. For some people who have this surgery, the tumor eventually returns. If this happens, you can have a second procedure to remove it again.

Radiation therapy after surgery can destroy parts of the tumor that weren’t removable with surgery. You can get radiation from a machine outside your body, or straight into the affected joint.

In people with diffuse TGCT, the tumor can come back many times, requiring multiple surgeries. People with this type of tumor may benefit from drugs called colony-stimulating factor 1 receptor (CSF1R) inhibitors, which block the CSF1 receptor to stop tumor cells from collecting.

CSF1R inhibitors include:

  • cabiralizumab
  • emactuzumab
  • imatinib (Gleevec)
  • nilotinib (Tasigna)
  • sunitinib (Sutent)

These drugs are still considered experimental. More research is needed to confirm what benefit, if any, they have for people with TGCT.

Although TGCT isn’t usually cancerous, it can grow to the point where it causes permanent joint damage and disability. In rare cases, the tumor can spread to other parts of the body and be life-threatening.

If you have symptoms of TGCT, it’s important to see your primary care doctor or a specialist to get treated as soon as possible.