The cause of a lump on the bone may possibly be a tumor, reports Healthline. Tumors can be either benign or malignant. A benign tumor is not cancerous but still may be dangerous and thus require treatment. Malignant tumors can spread throughout the body. Another possible cause is a bone cyst, notes WebMD. This is a fluid-filled lesion which develops inside the bone. It is not cancerous and usually heals on its own over time.
There are multiple types of benign and malignant bone tumors. Benign tumors are more common, with the most common being an osteochondroma, explains Healthline. This type accounts for approximately 35 to 40 percent of benign tumors. Osteochondromas occur most commonly in adolescents and teenagers, and usually develop near the actively growing end of long bones. An osteosarcoma is one of the most common malignant tumors, which usually develops around the hip, shoulder or knee.
A bone cyst most commonly affects children and young adults, reports WebMD. It may not present any additional symptoms. Unicameral bone cysts are the most common type, which usually develop in the upper arms and thighs. This may be caused by a fluid drainage problem in growing bones. A bone cyst often heals on its own as a child gets older, so bone cysts are quite rare in adults.