Cathepsin D in normal and neoplastic thyroid tissues

Background. Cathepsin D is a widely distributed lysosomal acidic endopeptidase. It is an estrogen-regulated protein that is a prognostic factor in breast cancer. The aim of this study was to measure cathepsin I) concentrations in thyroid tissues and to correlate these concentrations with clinical and pathologic parameters. Methods. Cathepsin D and thyroglobulin concentrations were measured in the cytosol of normal thyroid tissues (n = 14), benign nodules (n = 6), and thyroid carcinomas (n = 32) with an immunoradiometric assay. Statistical analysis was based on the Kruskal-Wallis and Wilcoxon tests and on the Spearman rank correlation coefficient. Results. The mean level of cathepsin D, expressed as picomoles per milligram protein minus thyroglobulin, was higher in the 32 carcinomas, 29.1 ± 15.5, than in the 14 normal thyroid tissues, 8.4 ± 2.5 (p < 0.001) or in the 6 benign nodules, 11.2 ± 7.3 (p = 0.00.3). Cathepsin D concentrations correlated with tumor size ; Spearman rank correlation coefficient was r s = 0.44 (p = 0.012). No significant difference was found regarding histologic type. Cathepsin D concentrations were inversely correlated with the thyroglobulin level in the tumor ; Spearman rank correlation coefficient was r s = -0.60 (p < 0.001). Conclusions. Cathepsin D concentration is higher in thyroid carcinoma than in normal thyroid tissue. increased cathepsin D concentrations correlate with thyroid tumor size but not with histologic type. Further studies should be done to confirm the potential prognostic value of cathepsin D in patients with thyroid carcinomas.