Beginning in early childhood, people with specific mutations on the Costello syndrome gene variant have an increased risk of developing certain cancerous and noncancerous tumors. Small growths called papillomas are the most common noncancerous tumors seen with this condition. They usually develop around the nose and mouth. The most frequent cancerous tumor associated with Costello syndrome is a soft tissue tumor called a rhabdomyosarcoma. Other cancers also have been reported in children and adolescents with this disorder, including a tumor that arises in developing nerve cells (neuroblastoma) and a form of bladder cancer (transitional cell carcinoma).