IMMUNOHISTOCHEMISTRY AS A PREDICTOR OF CLINICAL OUTCOME IN PATIENTS GIVEN POSTOPERATIVE RADIATION FOR SUBTOTALLY RESECTED PITUITARY-ADENOMAS

There is general agreement that postoperative radiation therapy is ben eficial for patients with subtotally resected pituitary adenomas. We h ave identified 41 such patients treated during a 20-year period who re ceived postoperative irradiation for a pituitary adenoma. The usual do se was 5040 cGy in 28 fractions. The mean follow-up time was 10.3 year s. On routine hematoxylin and eosin (H&E) staining, there were thirty- three chromophobe, seven eosinophilic, and one basophilic adenoma. Tis sue blocks were stained for growth hormone (GH), luteinizing hormone ( LH), thyroid-stimulating hormone (TSH), prolactin (PRL), and/or adreno corticotropin (ACTH) using the peroxidase-antiperoxidase immunohistoch emistry (IHC) method. Routine HandE staining was a poor predictor of t he IHC stain. While most patients with a known clinical endocrine synd rome stained positive on IHC for the suspected offending hormone, many patients without a clinical syndrome also stained positive indicating the presence of hormonally occult adenomas in this locally invasive g roup. The IHC stain results were compared to clinical outcome. The pre sence of positive GH IHC staining decreased the 15-year progression-fr ee survival (PFS) from 100% to 64% compared to GH negative adenomas (p = 0.06). There was a trend toward decreased 15-year PFS in patients w ho did not stain for LH. Positive staining for prolactin, ACTH, or TSH had no influence on the progression-free survival. We conclude that a dditional prognostic information can be obtained in this subset of pat ients (by performing IHC analysis) that is not known by the clinical p resentation or appearance on HandE stain.