Diffuse-Type Tenosynovial Giant Cell Tumors: Treatments and Progression Tenosynovial giant cell tumors (TGCT) - An Introduction Tenosynovial giant cell tumors (TGCT) are rare, locally invasive lesions of synovial origin that involve joints, tendon sheaths, and bursae. TGCT may be intra- or extra-articular and is classified by growth pattern and clinical presentation as