Neuroblastoma is a rare disease in which a solid tumor (a lump or mass caused by uncontrolled or abnormal cell growth) is formed by special nerve cells called neuroblasts. Normally, these immature cells grow and mature into functioning nerve cells. But in neuroblastoma, they become cancer cells instead.

Neuroblastoma most commonly starts in the tissue of the adrenal glands, the triangular glands on top of the kidneys that produce hormones responsible for controlling heart rate, blood pressure, and other important functions. By the time it is diagnosed, neuroblastoma has typically spread (metastasized) to other parts of the body, such as the bone marrow, lymph nodes, skin, liver, and bones. 

In a few cases, the tendency to get this type of cancer can be passed down from a parent to a child (familial type), but most cases of neuroblastoma (98%) aren't inherited (sporadic type). It happens almost exclusively in infants and children, and is slightly more common in boys than in girls.

Neuroblastoma most often affects children younger than 5 years, and most new cases occur in babies younger than 1 year old. It sometimes forms before birth but is usually found later, when the tumor begins to grow and cause symptoms. Approximately 10 new cases are diagnosed in Ireland each year.