Parathyroid carcinoma is an exceptionally uncommon endocrine neoplasm, accounting for less than 1% of parathyroid tumours and also a rare cause of primary hyperparathyroidism. Although this malignant lesion is usually slowly progressive, it is frequently associated with local recurrences and also with metastases involving the local lymph nodes or distant sites.
We present a 59-year-old male patient who developed a parathyroid carcinoma metastasis involving the anterior mediastinal lymph nodes and thymus remnants, 3 years after the primary tumour was identified and treated by surgical excision followed by chemo and radiotherapy. The patient presented with severe, symptomatic hyperparathyroidism and a gamma scan revealed increased uptake hyperfixation in the paratracheal lymph nodes. A lymphadenectomy was performed and the gross examination of the specimen showed a pinkish – white, firm, poorly circumscribed mass. The microscopic examination revealed an epithelial proliferation with a predominantly nodular/solid growth pattern, composed of cells exhibiting moderate nuclear pleomorphism, prominent nucleoli and high mitotic activity, involving two lymph nodes and thymus remnants. Upon immunohistochemical analysis, the proliferation showed positive staining for GATA 3, as well as a high Ki 67 index, whereas TTF 1 and thyroglobulin were negative in the tumour cells. Thus, the diagnosis of metastatic parathyroid carcinoma was established. The aim of this paper is to gain further knowledge about the histopathological and immunohistochemical features, as well as about the clinical behaviour of parathyroid malignant lesions, especially considering their rarity.