The updated staging system results in 36% of patients being reclassified to a lower stage, reducing overdiagnosis.
Evert van Velsen, MD, MSc, and colleagues in the Netherlands have found that the 8th edition of the American Joint Committee on Cancer/Tumor Node Metastasis (AJCC/TNM) staging system is superior to the 7th edition with regards to predicting overall survival (OS) and disease specific survival (DSS) in those with papillary thyroid cancer (PTC) and follicular thyroid cancer (FTC).Click through the slides below for details on their study and take home points for clinical practice.
Differentiated Thyroid Cancer TNM Staging. This year, the AJCC/TNM 8th edition staging system for DTC was introduced in clinical practice. The main differences between the 8th and 7th edition is that the 8th 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 7th edition of TNM classification and reclassified using the 8th 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 8th 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 7th or 8th editions. All patients in stage I of 7th edition stayed in stage I using 8th edition. The 8th edition showed better distinction between stages with regard to survival, but showed worse prognosis in stage II, III, and IV.
Take Home Points:
In patients with DTC, the AJCC/TNM 8th edition is a better predictor of OS and DSS vs 7th edition, regardless of DTC subclass
8th edition staging criteria results in 36% of patients being reclassified to lower stage, reducing over-diagnosis
Using 8th edition staging removes significant differences between PTC and FTC survival rates per stage
8th edition staging system better predictor of OS and DSS vs 7th edition for PTC and FTC
Perspective. "Undertaking reviews such as this one by van Velsen et al is an excellent way to monitor best practices and ensure that we aren’t ‘over practicing’ medicine. Regular examination and validation of guidelines based on new evidence and experience is necessary since best practice is, at best, a moving target. By reclassifying patients with DTC to lower stages while still predicting mortality accurately, the 8th AJCC/TNM guidelines should help reduce unnecessary treatments that are far from benign.”
