Tumors and cysts are extremely common in the hand.  The vast majority of these are entirely benign and can be treated by simple methods or, sometimes, by a simple surgery.
It is important, however, that tumors be evaluated by a knowledgeable physician to exclude the possibility of cancer.  In the hand these tumors may be either of the soft tissues or of the bones.
Very specific differences exist between a cancerous tumor and a benign cyst, and usually a differential diagnosis can be arrived at with a simple clinical examination.  Occasionally, a minor surgical procedure, removing some of the tissue, is needed to ascertain the difference.