Other names: GCTTS; Giant Cell Tumor of the Tendon Sheath; TSGCT

Tenosynovial giant cell tumors (TSGCTs) are rare, benign (not cancerous) tumors that involve the small or large joints causing pain, swelling and movement issues.

The parts within the joints that are affected include the tendon sheath (membrane that covers the tendon),  the bursae (fluid-filled sacs that form a cushion between bones, tendons and muscles) and the synovial membrane (a thin membrane that is the inner layer of the joint capsule).

The growth of the tumor damages and disrupts the surrounding structures and tissues causing the pain, stiffness and reduced joint motility. If the tumor is left untreated or recurs after treatment the damage can cause significant joint issues and disability.

Types of tenosynovial giant cell tumors:

Tenosynovial giant cell tumors can be separated into four different subtypes depending exactly where in the joint it is located and whether it is localized to one area or diffuse.

• Diffuse-type giant cell tumor
• Pigmented villonodular synovitis (PVNS)
• Intra-articular giant cell tumor of the tendon sheath
• Extra-articular giant cell tumor of the tendon sheath

Cause of tenosynovial giant cell tumors:

The tumor is caused by a change within the cell chromosomes called a translocation. This results in these affected cells making too much of a protein called colony stimulating factor-1 (CSF-1).  The CSF-1 protein attracts cells within the body that have a matching CSF-1 receptor including macrophages (a type of white cell) and several other types of cells. These cells that have the matching CSF-1 receptor accumulate and cause the bulk of the tumor, they are also thought to cause inflammatory changes in the affected area.

Diagnosis:

Diagnosis of TSGCT is often delayed as symptoms start off vague as pain and inflammation, and may mimic other joint injuries or conditions. 
The Doctor will need to take a detailed patient history, and identify relevant symptoms.  If TSGCT is suspected then specialized tests or imaging may be ordered including  X-rays, MRI (magnetic resonance imaging), sampling of synovial fluid and a biopsy to check what type of cells make up the tumor.

Treatment Options:

Surgery is the standard treatment for TSGCT with the goal being removal of the tumor from the joint area, however  complete removal is not always possible depending on the subtype, location and extent of the tumor.  Surgery can be open surgery when the area is opened up with an incision so the surgeon has full access to the joint.  Arthroscopic surgery which is done through a small incision may be an option in some cases of TSGCT.

Medications for TSGCT include Tyrosine Kinase inhibitors (TKI)  which selectively blocks the CSF-1 receptor. This stops the accumulation of macrophages and other cells in the affected area.
Turalio (pexidartinib). Due to known side effects of Turalio it is only used in selected patients who can not have surgery, have significant disease morbidity and they must be enrolled in a Risk Evaluation and Mitigation Strategy program (REMS)

Drugs used to treat Tenosynovial Giant Cell Tumor