context: A tumor is an abnormal growth of cells that serves no purpose. A benign tumor is not a malignant tumor, which is cancer. It does not invade nearby tissue or spread to other parts of the body the way cancer can. In most cases, the outlook with benign tumors is very good. But benign tumors can be serious if they press on vital structures such as blood vessels or nerves. Therefore, sometimes they require treatment and other times they do not. What causes a benign tumor to form? Often the cause is unknown. But the growth of a benign tumor might be linked to: Environmental toxins, such as exposure to radiation Genetics Diet Stress Local trauma or injury Inflammation or infection In many cases, benign tumors need no treatment. Doctors may simply use "watchful waiting" to make sure they cause no problems. But treatment may be needed if symptoms are a problem. Surgery is a common type of treatment for benign tumors. The goal is to remove the tumor without damaging surrounding tissues. Other types of treatment may include medication or radiation. There are many different types of benign tumors arising from different structures in the body. These are some of the most common types of benign tumors: Adenomas are benign tumors starting in the epithelial tissue of a gland or gland-like structure. The epithelial tissue is the thin layer of tissue covering organs, glands, and other structures. A common type of adenoma is a polyp in the colon. Adenomas might also grow in the liver or the adrenal, pituitary, or thyroid gland. If needed, adenomas can often be removed with surgery. Although not common, this type of tumor can become malignant. In the colon, less than 1 out of every 10 adenomas become cancerous. Fibromas (or fibroids) are tumors of fibrous or connective tissue that can grow in any organ. Fibroids commonly grow in the uterus. Although not cancerous, uterine fibroids can lead to heavy vaginal bleeding, bladder problems, or pelvic pain or pressure. Another type of fibrous tissue tumor is a desmoid tumor. These tumors can cause problems by growing into nearby tissues. Because they can cause symptoms, fibrous tissue tumors may need to be removed with surgery. Hemangiomas are a buildup of blood vessel cells in the skin or internal organs. Hemangiomas are a common type of birthmark, often occurring in the head, neck, or trunk. They may appear red or bluish in color. Most go away on their own. Those that interfere with vision, hearing, or eating may require treatment with corticosteroids or other medication. Lipomas grow from fat cells. They are the most common benign tumor in adults, often found in the neck, shoulders, back, or arms. Lipomas are slow growing, usually round and movable, and soft to the touch. They may run in families and sometimes they result from an injury. Treatment may be needed if a lipoma is painful or growing quickly. This may include steroid shots or removal through liposuction or surgery. Two other types of benign fat tumors are lipoblastomas, which occur in young children, and hibernomas. Meningiomas are tumors that develop from the membrane surrounding the brain and spinal cord. About nine in 10 are benign. Many grow slowly. Others grow more quickly. Treatment varies depending on the location of the meningioma and the symptoms it causes. Symptoms may include headache and weakness on one side, seizures, personality changes, and visual problems. Sometimes the doctor will choose to watch the tumor for a time. If surgery is needed, its success depends on your age, the location of the tumor, and whether it is attached to anything. Radiation treatment may be used for tumors that can't be removed. Myomas are tumors that grow from muscle. Leiomyomas grow from smooth muscle, which is found in internal organs such as the stomach and uterus. They can start in the walls of blood vessels. In the wall of the uterus, leiomyomas are often called fibroids. A rare benign tumor of skeletal muscle is rhabdomyoma. These tumors may be simply watched. To address symptoms, they may be shrunk with medication or removed with surgery. Nevi (moles) are growths on the skin. They can range in color from pink and tan to brown or black. You may develop new moles until about age 40. Moles that look different than ordinary moles (dysplastic nevi) may be more likely to develop into a type of skin cancer (melanoma). For this reason, it is important to have your skin checked regularly by a health care professional. This is especially true if your moles look unusual, grow or change in shape, have irregular borders, or change in color or in any other way. Sometimes it is necessary to remove a mole like this to check it for signs of cancer. Neuromas grow from nerves. Two other types of nerve tumors are neurofibromas and schwannomas. These benign nerve tumors can occur almost anywhere in nerves that run throughout the body. Neurofibromas are more common in people with an inherited condition called neurofibromatosis. Surgery is the most common type of treatment for benign nerve tumors. Osteochondromas are the most common type of benign bone tumor. These tumors usually appear as a painless bump or bumps near the joint such as the knee or shoulder. Often, the doctor will simply watch this benign tumor with X-rays. Surgery may be needed if the tumor causes symptoms such as pain or pressure on nerves or blood vessels. Papillomas are tumors that grow from epithelial tissue and project in finger-like fronds. They can be benign or malignant. They can grow in the skin, cervix, breast duct, or mucous membrane covering the inside of the eyelid (conjunctiva), for example. These tumors can result from direct contact with an infection such as human papillomavirus ( HPV). Some types of papillomas go away on their own. In some cases, surgery is needed to rule out cancer.