To describe the phenomenon of parathyroid gland involvement by thyroid carcinoma and to explore its clinicopathologic significance.
We reviewed the clinicopathologic features and described the histopathologic characteristics of 20 cases of parathyroid involvement found in a series of 911 papillary thyroid carcinomas.
Parathyroid involvement occurred in 3 patterns: (1) direct invasion from the main tumor with an infiltrative growth, (2) invasion of the parathyroid gland with an expansive growth and formation of a pseudocapsule between the carcinoma and the parathyroid gland, and (3) metastatic deposition within the parathyroid gland itself. Among the 20 cases, 6 (30%) had primary tumors measuring 1 cm or less, and 14 (70%) had primary tumors measuring more than 1 cm. The cases with smaller primary tumors had a comparatively lower rate of nodal metastasis (50% vs 100%, P =.02). Furthermore, none of the cases with smaller primary tumors had invasion of extrathyroid structures other than parathyroid gland, but such invasion was common among the cases with larger primary tumors (0% vs 71%, P =.01).
To the best of our knowledge, this is the first report showing that parathyroid involvement occurs in papillary thyroid carcinomas even in the early stage of the disease.