Clinicopathological spectrum, management, and outcome of ectopic parathyroid carcinoma: Experience with 24 cases

Ectopic parathyroid carcinoma (EPC) is a rare clinical entity with multiple diagnostic pitfalls, making surgical cures challenging. We assessed the clinicopathological spectrum and outcome of EPCs.

In this retrospective cohort study, 24 EPCs were identified from 133 PC patients treated at a tertiary referral center. The relationship between clinicopathological findings and locations was analyzed.

The locations of EPCs were predominantly intrathyroidal (62.5%), followed by 16.7% in the mediastinum, 8.3% in the retropharyngeal space, 8.3% in the carotid sheath, and 4.2% in the upper neck. Intrathyroidal EPC patients experienced higher serum calcium (p = 0.020), a higher rate of vascular invasion (p = 0.040), and a slightly higher incidence of non-R0 initial resection (p = 0.092) than those in other ectopic locations. Intrathyroidal EPC patients also suffered a trend of higher upper aerodigestive tract (UAT) invasion rate (p = 0.070) and higher risks of distant metastasis (p = 0.037) than the other PC patients. The 5-year disease-free survival rate after surgery was slightly compromised at 41.5% in intrathyroidal EPC patients compared with 77.8% among those in other ectopic locations (p = 0.143) and 59.7% among the other PC patients (log-rank = 3.194; p = 0.074), though without statistical significance.

Intrathyroidal EPC might cause a more biochemically and invasively distinct PC picture compared with other PCs. Special caution should be exercised in the preoperative diagnosis and management of such cases.