Cyclooxygenase-2 expression in human thyroid disease

Cyclooxygenase (COX)-2, which is the inducible form of the COX enzyme for prostaglandin synthesis and a key mediator of epithelial cell growth, has been shown to be up-regulated in gastrointestinal cancers. Additionally, regular intake of other non-steroidal anti-inflammatory drugs (NSAID) is known to decrease the incidence of these cancers. Therefore, the goals of the present study were to determine the possible involvement of COX-2 in human thyroid diseases.

We used immunohistochemical staining and Western blot analysis to characterize the expression of COX-2 proteins in thyroid tissues from 64 patients with thyroiditis, benign tumors, and malignant tumors with or without metastasis. Immunoreactivity scores were calculated by multiplication of the determined grades.

COX-2 proteins were not expressed in normal thyroid tissues. However, each type of tumor tissue showed intense bands of COX-2 protein expression in Western blot analyses, and the immunoreactivity scores were 7.67+/-1.17 (SD) for thyroiditis, 7.87+/-0.9 for benign tumors, 7.53+/-1.53 for follicular cancer, 7.63+/-1.11 for papillary cancer without metastasis, and 7.17+/-1.55 for papillary cancer with metastasis. No significant differences were found in the levels of COX-2 expression between different tumor tissue types.

No significant correlations were observed between clinical and/or pathological characteristics of thyroid tumors and the intensity of COX-2 protein expression. In addition, we found no difference in COX-2 protein expression between thyroiditis and thyroid tumors. Thus, up-regulation of COX-2 protein synthesis in human thyroid diseases does not appear to be of clinical significance.