Stage IV is divided into stages IVA, IVB, and IVC. In stage IVB, the tumor has spread to one or more lymph nodes that are larger than 6 centimeters (about 2 inches); or cancer has spread to the muscles or bones in the oral cavity (mouth), or to the base of the skull, and/or the carotid artery (blood vessel that carries blood from the heart to the head). Cancer may also have spread to one or more lymph nodes in the neck.