Tenosynovial Giant Cell Tumor, from the CureRays guide library.

Tenosynovial giant cell tumor is a benign but locally aggressive growth of the joint lining (also called PVNS) that can damage a joint; surgery is the mainstay, while new targeted pills and, in selected cases, radiation help when surgery alone isn't enough.

What it is.

Tenosynovial giant cell tumor (TGCT) is a benign — non-cancerous — but locally aggressive growth that arises from the synovium, the lining of joints, tendon sheaths, and the fluid-filled sacs (bursae) around joints. It is sometimes called pigmented villonodular synovitis (PVNS) when it affects a whole joint. It is driven by overproduction of a signaling protein called CSF1, which recruits inflammatory cells that build up into a mass. There are two main patterns: a small, localized nodule (most often on a finger, as 'giant cell tumor of the tendon sheath') and a diffuse form that involves a larger joint such as the knee or hip. Although it does not spread to other organs, the diffuse type can grow, cause swelling, pain, stiffness, and locking, and can erode the cartilage and bone of a joint over time. Treatment aims to remove the disease and protect the joint. When surgery cannot fully control diffuse disease, targeted medicines that block CSF1 signaling — and, in selected cases, radiation — are used.

How radiation treats it.

Radiation damages the DNA inside the overgrown synovial cells so they can no longer divide, while normal tissue repairs itself more effectively. In tenosynovial giant cell tumor, surgery and targeted medicines lead treatment, and radiation has a selective role — mainly for diffuse disease that surgery cannot fully clear — to lower the chance of recurrence. It can be delivered from outside the body in short, painless sessions, or, at some centers, by injecting a radioactive material into the joint to treat the lining from within. External radiation leaves no radioactivity in your body.

The ways we can treat it.

Radiation after incomplete surgery. For diffuse disease that cannot be completely removed, moderate-dose external radiation to the joint can reduce the chance of recurrence by treating the microscopic disease left behind.

Radiosynovectomy (injected radiation). In selected diffuse cases, a radioactive material is injected into the joint to treat the lining from within; this is used at some centers as an alternative or addition to external radiation.

Palliative / function-preserving radiation. Radiation can help control persistent or recurrent disease in a joint that is difficult to operate on, aiming to relieve symptoms and protect joint function.

Questions we hear often.

Is this cancer? No. Tenosynovial giant cell tumor is benign — it does not spread to other organs. However, the diffuse type can grow within a joint, cause pain and stiffness, damage cartilage and bone, and come back after surgery, so it is treated seriously. A malignant form exists but is extremely rare.

Why might I need a pill instead of (or in addition to) surgery? When the tumor diffusely involves a joint and surgery alone can't remove it all — or would cause serious functional loss — targeted CSF1R-inhibitor medicines like vimseltinib or pexidartinib can shrink the tumor and relieve symptoms. They are used for symptomatic disease that isn't suitable for surgery.

When is radiation used? Radiation is selective. It is mainly considered for diffuse disease that surgery cannot completely remove, to lower the chance of recurrence. Your team weighs that benefit against the long-term effects of radiating a joint, and will discuss whether external radiation or an injected (radiosynovectomy) approach fits your situation.

This guide is informational only. It is not medical advice — please confirm anything here with your care team.