TECHNETIUM-99M-SESTAMIBI PARATHYROID SCINTIGRAPHY - EFFECT OF P-GLYCOPROTEIN, HISTOLOGY AND TUMOR SIZE ON DETECTABILITY

The purpose of this study was to evaluate the effect of P-glycoprotein (P-gp) levels, predominant histology and tumor size on the detectabil ity of parathyroid adenomas with Tc-99m-sestamibi scans. Although prev ious studies have shown that positivity correlates with tumor size, fa lse-negative studies have been reported with large tumors and true-pos itives reported with very small tumors. Recent investigations have rep orted rapid washout of sestamibi in malignant tumors because of high l evels of P-gp, similar to that seen with multidrug chemotherapy resist ance. Therefore, we postulated that this mechanism might account for f alse-negative studies in parathyroid tumors. Preliminary reports have suggested that the predominant histological subtype influences positiv ity on 99mTc-sestamibi parathyroid scans, Methods: We studied 25 patie nts with surgically confirmed parathyroid adenomas with 99mTc-sestamib i parathyroid scans. The results of the imaging study were correlated with tissue P-gp levels, predominant histological subtype and size of the surgically removed glands. Results: There were 21 true-positive an d 4 false-negative results. The size of the adenomas ranged from 0.12 to 8.64 ml. We found no correlation between the results of the dual-ph ase Tc-99m-sestamibi study and either the predominant cell type or the level of P-gp. Positivity did correlate with the size of the adenoma (p = 0.73, p < 0.0001), We cannot exclude the possibility that P-gp an d cell type may still play a role in individual cases, but we suspect that other yet to be determined factors may influence 99mTc-sestamibi detectability in addition to tumor size.