Relationship between cell proliferation activity and morphological characteristics of papillary microcarcinoma in the thyroid of Graves' disease.

Three hundred and seven lesions of papillary microcarcinoma of the thyroid (PMT), found in 6830 cases of Graves' disease, were reviewed to evaluate the morphological characteristics. The prevalence rate and incidence of multiplicity of PMT in Graves' disease were higher (P < 0.05 and P < 0.005, respectively) in females (4.03% and 0.73%, respectively) than in males (2.68% and 0.12%, respectively). All lesions of PMT were classified histologically into three types: sclerosing non-encapsulated (SNE), non-sclerosing encapsulated (NSE) and non-sclerosing non-encapsulated (NSNE). Comparison of the three types of PMT revealed that the mean age and tumor size of NSNE were less than those of NSE and SNE (P < 0.001 and P < 0.005, respectively), and 13 of 19 lesions less than 1 mm belonged to NSNE. In addition, cell proliferation and expression of estrogen and progesterone receptors were examined immunohistochemically in 257 lesions of PMT. The Ki-67 labeling index of NSE was lower than that of NSNE and SNE (P < 0.005). None of the cases of PMT was positive for estrogen or progesterone receptors. The present study indicated that NSNE may be an early stage in tumor progression, and that fibrous encapsulation has the potential to modify neoplastic cell proliferation.