Extracapsular invasion of lymph node metastasis is an indicator of distant metastasis and poor prognosis in patients with thyroid papillary carcinoma

BACKGROUND: In patients with thyroid papillary carcinoma, age and the presence or absence of distant metastasis are regarded as the main prognostic factors. However, the histologic characteristics of thyroid papillary carcinoma that develops distant metastasis have not yet been clarified. METHODS: The histologic findings and prognosis of 50 patients with thyroid papillary carcinoma who later developed distant metastasis (metastatic group) were compared with those of 50 patients without local recurrence or distant metastasis (control group). The age, tumor size, and gender ratio of the control group were matched with those of the metastatic group. Univariate analyses (chi-square test and/or Fisher's exact test) and multivariate analyses (logistic regression) were performed. RESULTS: Univariate analyses showed that the incidence of nonpure papillary carcinoma, absence of bone at the periphery of the tumor, invasion of the perithyroidal muscle, large lymph node deposits, and extranodal invasion were significantly higher in the metastatic group. Multivariate analyses revealed that only extranodal invasion was statistically significant (P = 0.0045) and that the odds ratio of extranodal invasion in distant metastasis was 9. Moreover, the risk of death from thyroid carcinoma was higher among the patients with extranodal invasion than those without (P <0.01). CONCLUSIONS: The presence of extranodal invasion in patients with thyroid papillary carcinoma is an indicator of distant metastasis and poorer prognosis.