An extremely rare case of nonfunctioning parathyroid carcinoma occurring in a parathyroid adenoma.

A 53-year-old woman with a 4-month history of fatigue and somnolence was referred to her local doctor because of the worsening of her symptoms. Marked increases in her serum calcium (13.0 mg/dl) and intact-parathyroid hormone (175 pg/ml) were found, she was referred to our hospital. On physical examination, there was a palpable 3 cm mass in her right neck. Ultrasonography showed a 1.9 × 3.6 cm circumscribed hypoechoic lesion in the caudal right lobe of the thyroid gland. There was very mild 99mTc-sestamibi scintigraphic accumulation. Her preoperative diagnosis was primary hyperparathyroidism due to parathyroid carcinoma, and surgery was performed. The tumor weighed 6300 mg and did not invade the surrounding area. The pathology showed a mixture of small cells thought to be parathyroid adenomas and large, pleomorphic nuclei and fissionable carcinomas. Immunostaining showed that the adenoma portion was PTH-positive, chromogranin A-positive, p53-negative, PAX8-positive, PGP 9.5-negative with a Ki 67 labeling index (LI) of 2.2%. Whereas the carcinoma portion was PTH-negative, chromogranin A-negative, p53-positive, PAX8-positive, PGP 9.5-positive with a Ki67 LI of 39.6%, showing a nonfunctioning aspect and highly malignant. Postoperatively, the patient is alive without recurrence 9 years later without hypercalcemia or recurrence. A case of nonfunctioning parathyroid carcinoma in an extremely rare parathyroid adenoma is reported.