title: TNM classification of thyroid carcinoma.
abstract: BACKGROUND
  The understanding of biology of well-differentiated thyroid cancer has improved in the last two decades with the detailed understanding of prognostic factors and risk group stratification. The risk groups are crucial in the management of thyroid cancer and overall prognosis.
  The TNM staging system has been used in all human cancers, and it adheres to the biology of tumors. The data in thyroid cancer comes from retrospective studies, as there are no prospective randomized trials. The most recent TNM staging system was revised and published (6th edition) in 2002. The major attributes of the staging system include: age as the most important prognostic factor, and age is included in the staging system, below and above the age of 45; T1 tumors are considered to be those below 2 cm; T3 tumors include minor extrathyroidal extension invading the strap muscles; T4 tumors includes T4a and T4b, T4a being operable tumors; all anaplastic cancers are T4, although operable anaplastic thyroid cancers are considered to be T4a.
  
  
  CONCLUSIONS
  These changes in the TNM system are consistent with our current philosophy in the overall management of thyroid cancer and adjuvant therapy. The N staging system includes N1a and N1b-N1a being level VI lymph nodes, while N1b includes level IV and superior mediastinal and contralateral neck nodes. The TNM staging system helps reporting our data and comparing results in different parts of the world. However, there is no level I evidence in thyroid cancer.
authors.affiliation: Head and Neck Service, Memorial Sloan-Kettering Cancer Center, New York, NY, 10021, USA. shaha@mskcc.org
authors.forename: Ashok R
authors.initials: AR
authors.lastname: Shaha
mesh_terms: D019317:Evidence-Based Medicine; D006801:Humans; D009362:Neoplasm Metastasis; D009367:Neoplasm Staging; D011379:Prognosis; D018570:Risk Assessment; D013964:Thyroid Neoplasms / Q000145:classification / Q000473:pathology* / Q000601:surgery