Signet ring-like cells in pituitary adenoma.

We describe a case of non-functioning pituitary adenoma in a 35-year-old woman with a prior history of fertility problems. The patient had received clomiphen citrate and human chorionic gonadotrophin for 3 years. Histological examination of the tumor revealed signet ring-like cell areas admixed with minor conventional round-polygonal neoplastic cells. The two populations of tumor cells showed strong immunoreactivity for chromogranin and synaptophysin. The clinicopathologic features and diagnostic difficulties of this rare entity are discussed.