Oncocytic Transformation in Pituitary Adenomas: Immunohistochemical Analyses of 65 Cases

Abstract Context.—Oncocytic change in pituitary adenomas has been evaluated by electron microscopy and more recently by immunohistochemistry. The clinical significance of this change is not well known, although some reports suggest a relationship with more aggressive behavior. Objective.—To assess the frequency of oncocytic change in pituitary adenomas and to correlate this finding with clinicopathologic factors. Design.—We studied oncocytic change in a series of 65 pituitary adenomas by immunohistochemistry. According to the percentage of oncocytic cells stained by antimitochondrial antibody, adenomas were classified in 3 groups: 50% or more, 10% to 49%, and 1% to 9% of oncocytic cells. Results.—Eight cases (12.3%) showing at least 50% of oncocytic cells were classified as oncocytic adenomas: 6 were gonadotroph adenomas and 2 were null-cell adenomas. Among the remaining cases, 9 (14%; all gonadotroph adenomas) showed 10% to 49% oncocytic cells, and in 14 cases (21.5%; 5 gonadotroph adenomas, 6 somatotrop...