Osteoblastoma is a benign, bone-forming tumor that is extremely rare, accounting for only 1 percent of all primary bone tumors. Unlike most primary bone tumors, which favor the extremities, osteoblastoma occurs most often in the lower vertebrae of the spine or long bones of the lower extremity. It can, however, also occur in any of the bones of the arms, legs, hands and feet. Most of the time, osteoblastoma is not aggressive, but it can produce painful symptoms. One form of this tumor is considered aggressive because it is very likely to recur after incomplete surgical removal. No reported osteoblastoma has transformed into a malignant condition. The aggressive form does not metastasize (spread) to other parts of the body.