Refining the eighth edition AJCC TNM classification and prognostic groups for papillary thyroid cancer with lateral...

In the eighth edition, TNM staging system omits location of nodal metastasis as a criterion for staging patients with papillary thyroid cancer (PTC). Accordingly, all of non-metastatic N1b PTC patients are classified as stage I or II solely according to an age-cutoff of 55 years. We hypothesized that incorporating other lymph node (LN) factors into TNM staging system would better predict cancer-specific mortality (CSM) in N1b patients.

We enrolled 745 N1b PTC patients without distant metastasis. Alternative prognostic LN factors and cut-off points were assessed using Cox regression and time-dependent ROC analysis. Alternative prognostic groupings were derived based on minimal hazard differences for CSM among groups stratified by LN risk and age. We assessed accuracy of CSM prediction.

Lateral LN ratio (LNR) >0.3 and largest LN size >3 cm were prognostic factors for CSM. Stage II patients (eighth edition) with LN risk (lateral LNR >0.3 or largest LN size >3 cm) had a much higher CSM rate (20.9%) than those in the same stage without LN risk (3.2%). Alternative prognostic grouping (Group 1, <55 years without LN risk; Group 2, <55 years with LN risk or ≥55 years without LN risk; and Group 3, ≥55 with LN risk) achieved higher proportions of variance explained (PVEs) for predicting CSM (10.7%) than those of the eighth edition TNM staging system (4.8%).

The proposed grouping for N1b patients using LN risk can distinguish patients with poor prognosis from those with good prognosis better than the eighth edition TNM staging system.