Parathyroid carcinoma (PC) is a rare cause of primary hyperparathyroidism (PHPT), but requires distinct surgical management. This study compares clinical and biochemical features of PC and benign PHPT in a Korean cohort and evaluates the utility of traditional indicators, including the “>3 + >3 rule” (serum calcium >12 mg/dL and tumor size >3 cm) and elevated parathyroid hormone (PTH) levels, for preoperative suspicion of PC.

A retrospective analysis was conducted on 233 PHPT patients who underwent surgery at Gangnam Severance Hospital between 2005 and 2022, including 13 PC cases and 220 benign PHPT cases. Clinical, biochemical, intraoperative, and pathological findings and recurrence outcomes were compared.

PC patients had significantly higher PTH levels and larger tumors than benign PHPT patients. Serum calcium was higher in PC (12.3 vs. 10.9 mg/dL) but not statistically significant; only 4 (30.8%) of the PC patients exceeded 12 mg/dL, and 3 (23.1%) exceeded 14 mg/dL. Ionized calcium was also significantly higher in PC patients (1.6 vs. 1.4 mmol/L), though the absolute difference was small. Only 3 (23.1%) of the PC patients met both criteria of the “>3 + >3 rule”, and several benign cases also did, limiting specificity. Intraoperative features suggestive of malignancy were observed in 80% of PC patients lacking biochemical thresholds.

Western-derived biochemical thresholds, particularly serum calcium, appear insufficient to differentiate PC in Korean patients. Diagnostic strategies tailored for East Asian populations, integrating biochemical markers with intraoperative findings, are needed to enhance diagnostic accuracy and guide optimal surgical management.