Metastatic nonfunctioning parathyroid carcinoma: ultrastructural evidence of secretory granules and response to chemotherapy.

A 69-year-old woman was admitted to the hospital because of recurrent cervical nodules, a large anterior mediastinal mass, and malignant left pleural effusion. Light and electron microscopy of the resected cervical nodules and cytology of the pleural fluid showed findings consistent with parathyroid carcinoma. There was no evidence of hyperparathyroidism on clinical evaluation, multiple serum calcium and phosphorus determinations, skeletal survey, intravenous pyelogram, or radioimmunoassay of intact and carboxy-terminal parathyroid hormones in the serum. Electron microscopy revealed secretory granules in the cytoplasma of malignant cells. A dramatic and complete resolution of the mediastinal mass and pleural effusion occurred after 18 months of chemotherapy with "MACC" (methotrexate, adriamycin, cyclophosphamide and CCNU).