Mrozek E et al. (2006) Phase II study of celecoxib in metastatic differentiated thyroid carcinoma. J Clin Endocrinol Metab [doi: 10.1210/jc.2005-2498]

Cyclo-oxygenase 2 (COX2) is highly expressed in thyroid cancer tissue, compared with non-neoplastic and benign thyroid tissues, and inhibition of this enzyme has been shown to retard growth and progression of various tumors. Mrozek et al. report on a phase II clinical trial that evaluated the efficacy of a selective COX2 inhibitor, celecoxib, in patients with metastatic differentiated thyroid cancer (DTC) who had not responded to standard therapy.

This trial enrolled 32 patients with metastatic DTC and progressive disease, from two cancer centers in the US. Patients were given 400 mg celecoxib orally twice daily for 12 months, or until disease progressed. Clinical response to celecoxib was assessed every 12 weeks during treatment, by measurement of serum thyroglobulin levels, by CT imaging, or both. In all, 20 patients stopped taking the drug because of disease progression, and a further 3 stopped because of side effects. Of the remainder, only one patient who completed the study was progression-free at 12 months, and one patient had a partial response to treatment after 6 months. No serious adverse effects (including thromboembolic, cardiac, or gastrointestinal bleed) were observed.

The authors conclude that celecoxib is not associated with improved progression-free survival in patients with metastatic DTC. The authors speculate that the effect of celecoxib on tumor cells could be cytostatic rather than cytocidal, and suggest that COX2 inhibition might have an effect on early-stage cancers.