Currently, there is no laboratory test diagnoses parathyroid cancer (PTC) in the pre-operative period. A clinical presentation, with the combination of a significantly increased parathyroid hormone (PTH) and calcium levels, mainly allows to suspect PC in a patient with primary hyperparathyroidism (PHPT).

The aim was to evaluate the diagnostic value of parathyroid hormone level as a predictor of parathyroid cancer. Pre- and post-surgical examination data from 216 patients with PHPT was analyzed: I group (n=28) - with postoperatively confirmed PC; II group (n=188) - with parathyroid adenoma. The endpoints: 1) identify and analyze the diagnostic value of preoperative PTH levels in PTC prediction; 2) analyze correlation between tumor size, weight, and PTH levels in parathyroid adenomas and cancer.

The preoperative PTH levels was statistically significantly higher in I group vs. II group: 857.70 (618.60; 1581.39) pg/mL vs. 165.4 (117.98; 237.35) pg/mL, p<0,001. The ROC-analysis showed that the cut-off threshold at PTH > 502 pg/ml provides the best overall result of test efficiency: sensitivity - 0.857 (95% CI 0.728 - 0.987), specificity - 0.936 (95% CI 0.901 - 0.971), accuracy - 0.926, PPV - 0.667 and NPV - 0.978. The statistically confirmed correlations between tumor size, weight and PTH preoperatively were not found: r = 0,203 (-0,192; 0,541), p=0,309 and r = 0,314 (-0,113; 0,643), p=0,144, respectively.

The preoperatively increasing PTH level ≥ 502 pg/ml may potentially correspond to PTC presence in patients with PHPT. Surgery in this case should be planned on the principles of oncosurgery.