- In the 8th edition the definition of T3 has been revised (T3a tumors are more than 4 cm in the maximum dimension, limited to thyroid and T3b tumors of any size with gross extrathyroidal extension into the strap muscles). The difference between central and laterocervical neck lymph nodes and if stage IVc is not present is not considered. The age for poor prognosis has also changed from 45 to 55 years old