Thymus carcinoid producing parathyroid hormone (PTH)-related protein: report of a case.

We report herein the rare case of a thymus carcinoid producing parathyroid hormone (PTH)-related protein (PTHrP) found in a 43-year-old Japanese man who presented with a 19-month history of dyspnea. The diagnosis of a carcinoid was established by light microscopic, electron microscopic, 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 originated were found. After an excisional biopsy, which revealed PTH-related immunoreactivity in the tumor cells, 60 Gy of irradiation was delivered, resulting in a 48% reduction in the size of the tumor. Flow cytometry 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 pattern. To our knowledge, this is the first report of a carcinoid tumor in which positive staining for PTHrP by immunohistochemical methods was demonstrated.