Are Parathyroid Adenomas Typically Benign?
Yes, parathyroid adenomas are overwhelmingly benign tumors, with parathyroid carcinoma representing less than 1% of cases of primary hyperparathyroidism. 1
Benign Nature of Parathyroid Adenomas
Parathyroid adenomas account for approximately 80% of primary hyperparathyroidism cases and are benign neoplasms. 1, 2
Parathyroid carcinoma is exceedingly rare, occurring in less than 1% of primary hyperparathyroidism cases. 1
Even large parathyroid adenomas measuring over 6 cm in diameter can be benign despite their size. 3
The benign nature of these tumors is confirmed histopathologically, showing no evidence of malignant features such as capsular invasion or metastasis. 4, 3
Clinical Context and Hereditary Syndromes
In Multiple Endocrine Neoplasia Type 1 (MEN1), parathyroid adenomas are typically multi-glandular but remain benign, with primary hyperparathyroidism being the most common presenting feature (95% of MEN1 patients). 1
In CDC73-related (Hyperparathyroid-Jaw Tumor) syndrome, parathyroid carcinoma occurs in only approximately 15% of affected individuals, while single-gland parathyroid adenomas occur in over 70% of cases. 1
Loss of nuclear parafibromin staining by immunohistochemistry in parathyroid tissue should prompt consideration of CDC73 germline analysis, as this may help distinguish adenomatous from carcinomatous nodules. 1
Important Clinical Caveats
Biopsy of suspicious neck lesions in patients with CDC73-related syndrome is discouraged due to risk of seeding carcinomatous cells through the biopsy track. 1
Large adenomas are commonly considered more likely to be malignant, but size alone does not determine malignancy—histopathological examination is required for definitive diagnosis. 3
Severe clinical presentations with marked PTH and calcium elevations, large tumor size, and severe skeletal manifestations can mimic parathyroid carcinoma even when the tumor is benign (as seen with oxyphil parathyroid adenomas). 5
The diagnosis of primary hyperparathyroidism is made biochemically with serum calcium and PTH levels, not by imaging, which serves only for preoperative localization. 1, 2