Possible causes of a lump in the hand include ganglion cyst, inclusion cyst, carpal boss and enchondroma, according to About.com. It is also possible a lump in the hand is sarcoma, a type of cancer, but this is rare.
A ganglion cyst is the most common reason for a lump in the hand, and about 50 percent of all wrist or hand bumps fit into this category, explains About.com. These cysts form in the lining of the joint, and the wrist retains fluid. An inclusion cyst is another reason for a lump in the hand, and the cause of this is due to an injury in the hand. This cyst may appear years after the injury and often occurs after a penetrating injury such as a deep incision.
A lump in the hand may also refer to a carpal boss, which is an overgrowth of the bone of the hand, states About.com. Similar to a bone spur, some doctors misdiagnose this as a ganglion cyst, but the carpal boss is unmovable and firm. An enchondroma may also cause a lump in the hand, and this noncancerous tumor forms when cartilage begins to grow inside of the bone. This causes the bone to weaken, and in rare cases, the lump may develop into a cancerous tumor.