Subclassification of Tumor Extension and Nodal Metastasis in Papillary Thyroid Cancer to Improve Prognostic Accuracy of the Eighth Edition of the Tumor-Node-Metastasis Classification.

BACKGROUND

The eighth edition of the tumor-node-metastasis classification system (TNM-8th) reflects the prognosis of papillary thyroid cancer (PTC) better than the seventh edition. This study investigated methods to further improve the prognostic accuracy of the TNM-8th.

METHODS

We enrolled 5683 patients who underwent surgery for PTC at the Kuma Hospital. We subdivided tumor extension (T4a) into T4a1 and T4a2 based on intraoperative gross findings and N1 according to size ( < 3 cm and ≥ 3 cm) based on preoperative imaging findings.

RESULTS

The corresponding 20-year cancer-specific survival (CSS) rates of 4846, 403, 406, and 28 patients with TNM-8th stages I, II, III, and IVB, respectively, were 99.3%, 93.4%, 82.6%, and 11.3%. Owing to a CSS similar to that of stage II patients, N2 or T4a2 patients <55 years were upstaged to revised stage (re-stage) II. The CSS of stage III patients with T4a1 was significantly better (p < 0.0001) than that of those with T4a2, and the CSS of T4a1 patients was similar to that of stage II patients. Therefore, T4a1 patients ≥ 55 years were downstaged to re-stage II. Owing to a CSS similar to that of T4a2 stage III patients, N2 stage II patients were upstaged to re-stage III. The 20-year CSS was poorer in re-stage III (69.5%) than in stage III patients and similar in re-stage II patients (91.8%) and stage II patients.

CONCLUSION

Subdivision of clinical tumor extension and node metastasis further improves the TNM-8th for PTC and identifies poor risk patients more accurately.