A ganglion cyst is the most common type of tumor in the hand or wrist. It is a benign sac of gelatinous fluid that forms off a joint or tendon sheath. Cysts most often occur in the wrist but can appear around the finger joints.  Ganglion cysts form when a portion of the joint capsule or tendon sheath begins ballooning out and becomes filled with the fluid that lubricates the joint or tendon.

A giant cell tumor of tendon sheath is the second most common type of hand tumor. These tumors, unlike the fluid-filled ganglion cysts, are solid masses. They can develop anywhere near a tendon sheath. They are benign, slow-growing masses that spread through the soft tissue underneath the skin. These tumors are not cancer.

An epidermal inclusion cyst is another common type of tumor. It is also benign and forms underneath the skin. Epidermal inclusion cysts originate from the under-surface of the skin where there may have been a cut or puncture.  When skin cells, which create a protective waxy substance called keratin, get trapped under the surface, they continue to make keratin, which gets trapped under the surface of the skin. Overtime the keratin and the dead skin cells create a cyst.

Other less common types of hand tumors include lipomas (fatty tumors), neuromas, nerve sheath tumors, fibromas, and glomus tumors, among others.  Almost all are benign.