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Cancer starts when cells in the body begin to grow out of control and crowd out normal cells. Cells in nearly any part of the body can become cancer, and can then spread to other areas of the body. To learn more about cancer and how it starts and spreads, see What Is Cancer?

Neuroblastoma is a cancer that starts in certain very early forms of nerve cells, most often found in an embryo or fetus. (The term neuro refers to nerves, while blastoma refers to a cancer that starts in immature or developing cells). This type of cancer occurs most often in infants and young children.

The types of cancers that develop in children are often different from the types that develop in adults. To learn more about , see What Are the Differences Between Cancers in Adults and Children?

To understand neuroblastoma, it helps to know about the sympathetic nervous system, which is where these tumors start.

The sympathetic nervous system

The brain, spinal cord, and the nerves that reach out from them to all areas of the body are all part of the nervous system. The nervous system is needed for thinking, sensation, and movement, among other things.

Part of the nervous system also controls body functions we are rarely aware of, such as heart rate, breathing, blood pressure, digestion, and other functions. This part of the nervous system is known as the autonomic nervous system.

The sympathetic nervous system is part of the autonomic nervous system. It includes:

• Nerve fibers that run along either side the spinal cord.
• Clusters of nerve cells called ganglia (plural of ganglion) at certain points along the path of the nerve fibers.
• Nerve-like cells found in the medulla (center) of the adrenal glands. The adrenals are small glands that sit on top of each kidney. These glands make hormones (such as adrenaline [epinephrine]) that help control heart rate, blood pressure, blood sugar, and how the body reacts to stress.

The main cells that make up the nervous system are called nerve cells or neurons. These cells interact with other types of cells in the body by releasing tiny amounts of chemicals (hormones). This is important, because neuroblastoma cells often release certain chemicals that can cause symptoms (see Signs and Symptoms of Neuroblastoma).

Neuroblastomas

Neuroblastomas are cancers that start in early nerve cells (called neuroblasts) of the sympathetic nervous system, so they can be found anywhere along this system.

• Most neuroblastomas begin in the abdomen, either in an adrenal gland or in sympathetic nerve ganglia.
• Most of the rest start in sympathetic ganglia near the spine in the chest or neck, or in the pelvis.
• Rarely, a neuroblastoma has spread so widely by the time it is found that doctors can’t tell exactly where it started.

Some neuroblastomas grow and spread quickly, while others grow slowly. Sometimes, in very young children, the cancer cells die for no reason and the tumor goes away on its own. In other cases, the cells sometimes mature on their own into normal ganglion cells and stop dividing (which makes the tumor a benign ganglioneuroma - see below).

Other autonomic nervous system tumors in children

Not all childhood autonomic nervous system tumors are malignant (cancerous). Some tumors are benign (non-cancerous), and some can have both benign and cancer cells within the same tumor.

• Ganglioneuroma is a benign (non-cancerous) tumor made up of mature ganglion and nerve sheath cells.
• Ganglioneuroblastoma is a tumor that has both malignant and benign parts. It contains neuroblasts (immature nerve cells) that can grow and spread abnormally, similar to neuroblastoma, as well as areas of more mature tissue that are similar to ganglioneuroma.

If a child is thought to have one of these tumors, it is usually removed by surgery and looked at carefully with a microscope to see if it has areas of cancer cells (which would make it a ganglioneuroblastoma). If the final diagnosis is ganglioneuroma, no other treatment is needed. If it’s found to be a ganglioneuroblastoma, it’s treated the same way as a neuroblastoma.