Immunohistochemical detection of somatostatin receptor (SSTR) subtypes 2A and 5 in pituitary adenoma from acromegalic patients: Good correlation with preoperative response to octreotide

Objective The aim of this study was to determine the correlation between the expression of somatostatin receptors by immunohistochemistry and the percent suppression of GH levels in the octreotide suppression test. Patients and Methods Twenty-two patients with acromegaly who underwent an octreotide suppression test before surgery were studied. We performed immunohistochemistry for Somatostatin receptor 2A (SSTR2A) and Somatostatin receptor 5 (SSTR5) on the surgical specimens from all patients, which we scored according to the number of tumor cells staining positive at the surface membrane (3+: >50%, 2+: 25-50%, 1+: <25%). We sought correlations of percent suppression in the octreotide suppression test with these immunohistochemistry scores. Results Somatostatin receptor 2A (SSTR2A) showed the highest frequency of score 3+ (13 of 22, 59.1%) by immunohistochemistry. Subtype 5 showed the highest frequency for score 2+ (9 of 22, 40.9%), and one (4.5%) was immunonegative. For subtype 2A, there was a significant correlation with percent decrease (P=0.002< 0.01). In contrast, there was no significant correlation for SSTR5. Conclusion Immunohistochemistry for SSTR2A in pathology specimens from acromegalic patients enabled selection of those experiencing clinical benefit from octreotide. Therefore, performing immunohistochemistry for detection of SSTR2A is recommended for all specimens obtained by surgery.