PROLACTIN-PRODUCING PITUITARY-TUMOR - RESISTANCE TO DOPAMINE AGONIST THERAPY

A 14-year-old girl presented with a rapidly growing, invasive prolacti n-producing pituitary tumor that failed to respond to dopamine agonist medication. Histological,immunocytochemical, and ultrastructural stud ies of the surgically removed tissue revealed a pleomorphic, chromopho bic, or slightly acidophilic pituitary tumor that was immunoreactive f or prolactin and that, according to electron microscopy, consisted of atypical lactotrophs showing no evidence of cell shrinkage. In situ hy bridization demonstrated large amounts of prolactin messenger ribonucl eic acid (mRNA), moderate amounts of estrogen receptor mRNA and dopami ne (D-2) receptor mRNA, and an absence of growth hormone mRNA in the t umor cells. Because D-2 receptor mRNA was present in the tumor, causes other than D-2 receptor loss may have been responsible for the resist ance of the lactotrophs to dopamine agonist administration.