Updated AJCC/TNM Staging Better Predictor of Survival in Thyroid Cancer

Differentiated Thyroid Cancer TNM Staging. This year, the AJCC/TNM 8^th edition staging system for DTC was introduced in clinical practice. The main differences between the 8^th and 7^th edition is that the 8^th edition raised the age cutoff from 45 to 55 years, removed minor extrathyroidal extension from definition of T3 tumors, and N1 disease authomatically results into stage II instead of III or IV.

The Study. The retrospective review looked at adults diagnosed with PTC or FTC in the Netherlands between 2002 and 2016. Disease characteristics included disease type, TNM stage, presence/absence of multifocal disease, and minor/gross extrathyroidal extension. Treatment data consisted of extent of surgery and use of RAI. Patients were categorized according to the 7^th edition of TNM classification and reclassified using the 8^th edition for the current study; final analysis included 792 patients. 

The Results. PTC was present in 628 patients with the remaining 164 patients having FTC, including 55 patients with Hürthle cell carcinoma; 106 patients died with 57 that died due to DTC. Patients with FTC were significantly older (46.7 vs 56.5 years) and had a significantly higher mortality rate. Patients with FTC had distant metastases significantly more often at presentation and a total or hemithyroidectomy was performed in 773 patients and 736 patients received RAI. 

Results (continued). Applying the 8^th edition staging criteria, 282 patients were reclassified into a lower stage and patients with FTC were reclassified more often vs those with PTC (49% vs 32%). For DTC (and PTC and FTC separately) stage at diagnosis was significantly related to OS and DSS using 7^th or 8^th editions. All patients in stage I of 7th edition stayed in stage I using 8th edition. The 8^th edition showed better distinction between stages with regard to survival, but showed worse prognosis in stage II, III, and IV.