There has been much recent investigation of the
cyclooxygenase (Cox)
enzymes in
tumor biology, but, to our knowledge, no study has yet been published describing Cox activity in
medullary carcinoma of the thyroid (MTC). Nine cases of MTC from the past 10 yr were retrieved from our hospital archives. Slides cut from
formalin-fixed
paraffin-embedded
tumor tissue from these cases were assessed for the activities of Cox-1 and Cox-2
enzymes by immunohistochemistry as well as by a battery of immunohistochemical stains for intermediate filaments,
peptide hormone, and proliferation and promoter
antigens. The staining reactions were semiquantitatively assessed and scored for comparison with each other as well as with each patient s clinical presentation and course. Staining for Cox-1 and Cox-2
enzymes was present only in tumorous tissue, not in nontumorous thyroid tissue or C-cells. Cox-2 staining was not consistently increased over Cox-1 staining; however, Cox-2 staining bore statistically significant correlations with the expression of low molecular weight
keratin, thyroid-transforming factor-1, topoisomerase, and MIB1. Hyperplastic C-cells from patients with diverse physiologic conditions and from three patients with C-cell
hyperplasia accompanying
medullary carcinoma or
multiple endocrine neoplasia type IIa showed no reactivity for the Cox
antibodies. It appears that Cox
enzyme immunoreactivity is present only in the neoplastic C-cells of
medullary carcinoma, but with variable expression. A practical application of the preceding finding might involve the use of Cox staining to distinguish invasive
medullary carcinoma cells from hyperplastic C-cells.