Expression of the Calcium-Sensing Receptor on Normal and Abnormal Parathyroid and Thyroid Tissue.

[INTRODUCTION] Current imaging techniques have several limitations in detecting parathyroid glands. We have investigated the calcium-sensing receptor (CaSR) as a potential target for specifically labeling parathyroid glands for radiologic detection. For accurate imaging it is vital that a large differential expression exists between the target tissue and adjacent structures. We sought to investigate the relative abundance of the CaSR in normal and abnormal parathyroid tissue, as well as normal and abnormal thyroid.

[METHODS] Existing clinical specimens were selected that represented a wide variety of pathologically and clinically confirmed malignant and benign thyroid and parathyroid specimens. Sections were stained for the CaSR using immunohistochemistry and scored for intensity and abundance of expression. (H score = intensity scored from 0 to 3 multiplied by the % of cells at each intensity. Range 0-300).

[RESULTS] All parathyroid specimens expressed the CaSR to a high degree. Normal parathyroid had the highest H score (271, s.d. 25.4). Abnormal parathyroid specimens were slightly lower but still much higher than normal thyroid (H score 38.3, s.d. 23.3). Medullary thyroid cancer also expressed the CaSR significantly higher than normal thyroid (H score 182, s.d. 69.1, P < 0.001) but below parathyroid levels. Hürthle cell carcinoma expressed the CaSR to a lesser degree but higher than normal thyroid (H score 101, s.d. 46.4, P = 0.0037).

[CONCLUSIONS] The CaSR is differentially expressed on parathyroid tissue making it a feasible target for parathyroid imaging. False positives might be anticipated with medullary and Hürthle cell cancers.