THYMUS CARCINOID PRODUCING PARATHYROID-HORMONE (PTH)-RELATED PROTEIN - REPORT OF A CASE

We report herein the rare case of a thymus carcinoid producing parathy roid hormone (PTH)-related protein (PTHrP) found in a 43-year-old Japa nese man who presented with a 19-month history of dyspnea. The diagnos is of a carcinoid was established by light microscopic, electron micro scopic, and immunohistochemical examinations. The tumor was considered to be thymic in origin because of its anatomic location, the presence of feeders to the tumor (derived from the internal thoracic arteries) , and the fact that no other tumors from which it could have originate d were found. After an excisional biopsy, which revealed PTH-related i mmuno-reactivity in the tumor cells, 60 Gy of irradiation was delivere d, resulting in a 48% reduction in the size of the tumor. Flow cytomet ry showed a diploid DNA pattern, with 94% of the cells in the G1 phase , 4% in the S phase, 2% in the G2+M phase, and a G2+M/G1 ratio of 1.95 . The primary cell culture showed some cells adopted in a cord-like pa ttern. To our knowledge, this is the first report of a carcinoid tumor in which positive staining for PTHrP by immunohistochemical methods w as demonstrated.