Prognostic significance of metastatic lymph node size and extra-nodal extension in papillary thyroid carcinoma according to the 9th edition of general rules for the description of thyroid cancer risk stratification: a single center validation study.

[PURPOSE] In the 9th edition of general rules for the description of thyroid cancer (GRDTC), the N factor was subdivided according to the maximum diameter of metastatic lymph nodes, presence of extra-nodal extension (ENE), and location of mediastinal lymph nodes. This study aimed to investigate the clinical usefulness of the 9th GRDTC risk stratification in papillary thyroid carcinoma (PTC) patients with lymph node metastasis.

[METHODS] A total of 703 PTC patients with lymph node metastasis who underwent initial thyroidectomy at our institution between January 2000 and October 2023 were included.

[RESULTS] Among the 703 patients with PTC, the 10-year cause specific survival rates of patients with pN1a-1 (n = 383), pN1a-2 (n = 13), pN1b-1 (n = 234), and pN1b-2 (n = 73) were 97.9%, 100%, 95.4%, and 76.2%, respectively (p < 0.001). Therefore, the pN1b-2 classification identified patients with a worse prognosis among those with pN1b. Among the 664 patients with M0 PTC, the 10-year disease free survival (DFS) rates of the patients with pN1a-1 (n = 378), pN1a-2 (n = 13), pN1b-1 (n = 215), and pN1b-2 (n = 58) were 86.9%, 62.5%, 79.9%, and 59.4%, respectively (p < 0.001). The pN1b-2 category was associated with worse DFS in pN1b patients.

[CONCLUSIONS] The 9th edition of the GRDTC may be useful for stratifying the prognosis of patients with PTC. The risk assessment of PTC-related death and recurrence will be more accurate by considering the size of lymph node metastasis and ENE in GRDTC.