Primary and Metastatic Parathyroid Malignancies: A Rare or Underdiagnosed Condition?

Objective: Parathyroid gland malignancies are considered rare. The most common of these tumor types is primary parathyroid carcinoma. Metastatic spread from other cancers may also occur with up to 10% of cancers from other sites showing parathyroid involvement at autopsy. Tumor-to-tumor metastases (metastatic spread to parathyroid neoplasm) from remote cancers to the parathyroid gland have been described. Methods: We did a PubMed literature review and analysis of our own experience of 392 consecutive parathyroidectomies. Results: Primary and secondary parathyroid malignancies can be grouped into three categories: primary parathyroid carcinoma (PPCa), spread of carcinoma into parathyroid glands by contiguous extension from the thyroid gland or other head and neck cancer, and metastatic disease to the parathyroid gland from distant cancers. Studies of tumor-to-tumor spread indicate a predilection of spread to endocrine tumors possibly because of the rich blood supply that is present in endocrine tumors. Two of our 392 parathyroidectomies (0.5%) had cancer: one metastatic (thymic neuroendocrine tumor) and another PPCa. Conclusion: Metastatic disease to the parathyroid gland is poorly documented. When performing surgery for primary thyroid cancer, the search for parathyroid gland metastases is often overlooked because of the desire to preserve parathyroid function. Metastatic disease from other cancers to a benign parathyroid gland or to a parathyroid adenoma probably suggests a grave prognosis because it likely indicates widespread metastatic disease; however, isolated metastases to the parathyroid may occur. Although these lesions may be uncommon they may not be as rare as once thought.