Simplifying the TNM system for clinical use in differentiated thyroid cancer

The TNM stratification has been found useful at stratifying patients with differentiated thyroid carcinoma (DTC) into prognostic risk groups. However, it is cumbersome to implement clinically given the large number of bins within this system and the complicated system of arriving at stage information.

We decided to quantify each variable in this system to arrive at a simplified quantitative alternative to the TNM system (QTNM) and compare this with the conventional system. We used our electronic record system to identify 614 cases of DTC managed at our institution from 1987 to 2006. Cancer-specific survival (CSS) and disease-free survival (DFS) were calculated by the Kaplan-Meier method, and a simplified QTNM score was devised using a Cox proportional hazards model.

We were able to quantify the TNM system as follows: 4 points each for age older than 45 years and presence of neck nodal metastases while 6 points for tumor size larger than 4 cm or extrathyroidal extension and 1 point for nonpapillary DTC. A sum of 0 to 5 points was low risk, 6 to 10 points intermediate, and 11 to 15 points high risk. Comparison with the conventional TNM system and two other systems revealed similar or better discrimination with the QTNM and this discrimination was maintained when this risk stratification was applied to a unique validation set.

The QTNM system as opposed to the conventional TNM system seems to be a simple and effective method for risk stratification for both recurrence and cancer-specific mortality.