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Lymph node metastasis is an important clinicopathological feature of papillary thyroid carcinoma (PTC). PTC having clinically apparent lateral node metastasis detectable on preoperative imaging studies (N1b) is known to show a dire prognosis. However, N1b cases include various levels of biological aggressiveness, depending on the size, number, laterality and invasiveness of metastatic nodes. We investigated differences in the prognoses of 621 N1b patients based on these features and compared their prognoses with those of 4297 patients without clinically apparent metastasis (N0) and 125 patients with clinically apparent central node metastasis only (N1a). Disease-free survival (DFS) and cause-specific survival (CSS) of N1b or N1a patients were significantly worse than those of N0 patients, but the prognosis of N1b patients did not differ from that of N1a patients. In the subset of N1b patients, metastatic nodes larger than 3cm, extranodal extension, or 5 or more clinically apparent metastatic nodes independently affected DFS and a combination of the former two features also showed an effect on CSS on multivariate analysis. Prognosis of N1b patients who had none of these features did not differ from that of N1a patients. It is therefore suggested that N1b patients having metastasis larger than 3cm, those showing extranodal extension, and those having 5 or more clinically apparent metastasis should regarded as high-risk, and that careful surgical treatment and postoperative follow-up are necessary.
Ito et al. (Thu,) studied this question.