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 beneficial for patients with subtotally resected pituitary adenomas. We have identified 41 such patients treated during a 20-year period who received postoperative irradiation for a pituitary adenoma. The usual dose was 5040 cGy in 28 fractions. The mean follow-up time was 10.3 years. On routine hematoxylin and eosin (H&E) staining, there were thirty-three chromophobe, seven eosinophilic, and one basophilic adenoma. Tissue blocks were stained for growth hormone (GH), luteinizing hormone (LH), thyroid-stimulating hormone (TSH), prolactin (PRL), and/or adrenocorticotropin (ACTH) using the peroxidase-antiperoxidase immunohistochemistry (IHC) method. Routine H&E staining was a poor predictor of the IHC stain. While most patients with a known clinical endocrine syndrome 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 group. The IHC stain results were compared to clinical outcome. The presence of positive GH IHC staining decreased the 15-year progression-free 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 who did not stain for LH. Positive staining for prolactin, ACTH, or TSH had no influence on the progression-free survival. We conclude that additional prognostic information can be obtained in this subset of patients (by performing IHC analysis) that is not known by the clinical presentation or appearance on H&E stain.