Tenosynovial cysts are not usually cancerous over time. Most tendon sheath cysts are benign cystic lesions caused by factors such as chronic inflammatory irritation of the tendon sheath. These cysts develop slowly and basically do not become malignant, and there may be no obvious clinical symptoms when the cysts are small, but when symptoms such as joint pain occur, you should seek medical attention in time for your doctor to determine whether surgery is needed.