BACKGROUND.
The majority of patients with thyroid microcarcinoma have a favorable prognosis. However, some patients may die from this tumor. Although the incidence of microcarcinoma is high, to the authors' knowledge no histologic risk factors have been identified. The objective of this study was to establish risk factors for patients with thyroid microcarcinoma.
METHODS.
The histologic findings for 1743 surgically excised thyroid microcarcinomas (Յ10 mm in greatest dimension) and simultaneously obtained lymph nodes from 324 microcancer patients were reexamined to determine risk factors. Follow-up for the patients was 11.2 Ϯ 6.3 years (mean Ϯ standard deviation). These thyroid carcinomas were classified according to the World Health Organization Histological Classification system, and lymph node involvement was classified into two groups: those patients with extracapsular invasion of the lymph node metastasis (ECI) (62 patients) and those patients without (1681 patients). A Fisher exact test, an F test, univariate and multivariate proportional hazards regression analyses, and a Kendall correlation measurement were performed.
RESULTS.
No undifferentiated tumors were found among the microcarcinomas.
During the follow-up period, 1643 of 1743 patients were alive without recurrence, 25 were alive with recurrence, 71 had died of thyroid-unrelated diseases including 2 patients with recurrence, and 4 had died of recurrent thyroid carcinoma. In total, recurrence was noted in 31 patients. Multivariate proportional hazards regression analysis revealed that the absence of Graves disease (risk ratio ϭ 5) and the presence of ECI (risk ratio ϭ 7) were significant risk factors for disease recurrence.
Univariate analysis revealed that patient age and the presence of ECI were significant risk factors for thyroid carcinoma-related deaths.
CONCLUSIONS.
The presence of ECI of lymph node metastasis in patients with thyroid microcarcinoma was found to be a significant indicator of disease recurrence and a poorer prognosis.