Plasminogen activation system in active even in thyroid tumors; an immunohistochemical study.

The plasminogen activation system is one of the prominent factors in tumour progression since it enhances both distant metastasis and direct invasion. In this study we investigated the expression and localization of this system in clinical thyroid tumours. It was found that urokinase-type plasminogen activator (uPA), its receptor (uPAR) and plasminogen activator inhibitor type 1 (PAI-1) were expressed diffusely in most thyroid carcinomas. The lesions positive for the latter two were equal to or sometimes even a litter more extensive than those positive for uPA. The immunoreactivity of plasminogen activator inhibitor type 2 (PAI-2), however, was often partially or even entirely absent, and only 56% of the carcinomas expressed it diffusely, indicating that the two types of inhibitors in this carcinoma have quite different characteristics. No relationship between the expression of these proteins and clinicopathological parameters could be determined. THese findings suggest that the plasminogen activation system is functionally active in thyroid carcinoma but that is has hardly any effect on its general characteristics, that is, slow growth and excellent prognosis of usual types and the exceptionally sudden progression of the anaplastic type. In benign tissues, too, this system was often expressed and appeared to enhance their growth to some extent.