The eighth edition of the TNM classification system was announced. Thyroid cancers were included in the fourth edition of the TNM classification system which was published in 1987. Each version of the TNM system which is updated based on evidence in the literature, includes some important differences from the previous version for the differentiated thyroid carcinomas (DTCs), like other cancers. Seventeen different classification systems for thyroid cancer have been developed until today. Some of these systems are quite complex and are difficult to use in practice. It has been shown that the TNM system with the new regaulations is the most consistent and applicable staging system for DTC in different patient groups, and the TNM system is now the most commonly used classification system in thyroid cancer, as in other cancer types.
The most important update of the eighth version is that the age as prognostic factor is regulated as younger and older than 55 years, which has been divided as younger/older than 45 years of age in prior editions. Furthermore, the change in the definition of T3 in the T stage is remarkable. In the seventh edition, the definition of minimally invasive extrathyroidal extension and the definition of perithyroidal soft tissue included in its example have been abolished. Macroscopic extension into any of the strap muscles was moved to the T3 category in the eighth edition. In N staging in the 7th edition, the upper mediastinal lymph node involvement which took place in N1b was moved to the N1a category. In the eighth edition, it is observed that generally in patients over 55 years old have a stage downgrade in all stages compared to the seventh edition.
In the eighth edition, the appropriate tumor stage can easily be determined. In patients under the age of 55 years, patients with distant metastases were defined as stage II, and without as stage I. Patients with distant metastasis over the age of 55 years are defined as stage IVB. The stages of patients without distant metastases over the age of 55 years can be defined by other clinical features (intrathyroidal tumor, macroscopic extrathyroidal extension, lymph node metastasis and distant metastasis). If there is no lymph node metastasis in patients with intrathyroidal tumors smaller than 4 cm (T1,T2), it is called stage 1, and stage II, if lymph node metastasis is present. Patients with intrathyroidal tumors greater than 4 cm (T3) are placed in stage II, regardless of lymph node status (N0 or N1). In tumors with macroscopic extrathyroidal extension; irrespective of the lymph node metastasis, the tumor is in stage II if only invasive into the strap muscles, and stage III if extended to subcutaneous tissue, larynx, trachea, recurrent laryngeal nerve and esophagus, and stage IVA if extended to the prevertebral fascia, mediastinal vessels or if surrounded carotid artery.
TNM classification is a staging system that reliably predicts disease-specific survival in the DTC. The eighth edition of TNM compared to the previous editions classifies a large proportion of patients with DTC in low-risk groups in terms of mortality, and initial evaluations show that it may be more suitable in predicting disease-specific survival.
Key words: differentiated thyroid carcinomas, TNM classification system, TNM eighth version
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