A solid tumor is an abnormal mass of tissue that can occur in all different parts of the body including the brain, kidneys, liver and bones. The two major types of solid tumors are sarcomas and carcinomas. Sarcomas are tumors that occur in blood vessels, bones, fat tissue, ligaments, lymph vessels, muscles or tendons. The most common solid tumors in children and teens are rhabdomyosarcoma, neuroblastoma, Wilms Tumor, germ cell tumors and retinoblastoma.