Brain tumors are the most common solid tumors in children. Approximately 2,200 children in the US are diagnosed with a brain tumor each year. Brain tumors, either malignant or benign, are tumors that originate in the cells of the brain. A tumor is an abnormal growth of tissue. A benign tumor does not contain cancer cells and usually, once removed, does not recur. Most benign brain tumors have clear borders, meaning they do not invade surrounding tissue.