To increase our knowledge of the basic biological mechanisms of thyroid lesions, growth activity(GA) in 63 thyroid tumors was evaluated by immunohistochemical stain using monoclonal antibody MIB-1 which represents growth activity bi its positive cell rates. The results obtained were summarized as follows. The MIB-1 positive cell rate of normal tissue(0.18%) was very low and significantly lower than that of follicular adenoma(1.91%). The MIB-1 positive cell rate of thyroid carcinomas was significantly higher than that of follicular adenoma or normal tissue. Of the thyroid carcinomas, the highest MIB-1 positive cell rate was observed in undifferentiated carcinoma(29.33%), followed by follicular carcinoma(8.95%), medullary carcinoma(8.16%), papillary carcinoma(3.54%) in order their MIB-1 positive cell rate. Statistically significant differences of MIB-1 pasitive cells were noted among various types of thyroid carcinomas with two exceptions between medullary carcinoma and papillary carcinoma, or between medullary carcinoma and follicular carcinama. Of the follicular tumors, the MIB-1 positve cell rate was obserbed in 12.40% of widely invasive follicular carcinoma, in 5.89% of minimally invasive follicular carcinoma, in 3.26% of solid/trabecular adenoma, and in 0.90% of normo/macrofollicular adenoma. Significant difference of MIB-1 positive cell rate were found between various subtypes of follicular tumors. In papillary tumors, the MIB-l positive cell rate of overt papillary carcinoma(5.32%) was significantly higher than that of occult papillary carcinoma(1.25%). Our findings suggest that immunohistochemical evaluation using the antibody MIB-1 contributes to the understanding of growth characteristics and biological activities in thyroid tumors.
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