GH responsiveness to corticotropin-releasing hormone identifies corticotroph-like somatotroph adenomas in acromegaly

PURPOSE: Corticotropin-releasing hormone (CRH) induces an increase in growth hormone (GH) secretion in a subset of patients with acromegaly; however, the characteristics of these CRH responders remain poorly defined. METHODS: 22 CRH responders were retrospectively compared with 43 nonresponders. RESULTS: CRH responders exhibited significantly larger tumors and more frequent visual field impairment than nonresponders, despite comparable baseline GH and insulin-like growth factor 1 (IGF-1) levels, and disease duration. Tumor volume and diameter were positively correlated with the GH increase ratio in CRH test, whereas GH and IGF-1 per tumor volume or diameter were significantly lower in CRH responders, indicating reduced GH secretory capacity relative to tumor size. Immunohistochemical analyses revealed higher corticotropin-releasing hormone receptor 1 (CRHR1) and lower CRHR2 expression in CRH responders. In addition, T-box transcription factor (TPIT) and adrenocorticotropic hormone (ACTH) expression were significantly more frequent in adenomas from CRH responders, suggesting a corticotroph-like phenotype. GH responses to CRH were significantly correlated with those to luteinizing hormone-releasing hormone but not thyrotropin-releasing hormone or oral glucose tolerance testing. GH responses to CRH tended to be inversely correlated with somatostatin receptor subtype 2 expression as a predictor of first-generation somatostatin receptor ligand efficacy but not with octreotide response or MRI signal intensity. CONCLUSIONS: These findings support that GH responsiveness to CRH identifies a biologically distinct subset of somatotroph adenomas characterized by corticotroph-like features, larger tumor size, and reduced GH secretory capacity. GH responsiveness to CRH may serve as a noninvasive indicator of intrinsic tumor biology and behavior.