Professor, Small Animal Internal Medicine University of Florida Gainesville, Florida, United States
Disclosure(s):
Chen Gilor, DVM, PhD, DACVIM: Baycom Diagnostics: Baycom supplied materials to research projects I've been conducting (Ongoing)
Abstract:
Background: The ACTH stimulation test is traditionally used in dogs with suspected hypercortisolism; but its utility in pre-treatment discrimination of benign and malignant adrenocortical tumors and pheochromocytomas is uncertain. We hypothesized that a positive response to ACTH stimulation (StimPos) would be most frequent in adenomas, less in carcinomas, and least in pheochromocytomas.
Objective: To determine if the ACTH stimulation test can discriminate canine adrenal tumor types using histopathology as gold-standard. Animals: One hundred and twenty-one dogs with histologically diagnosed adrenal tumors and pre-treatment ACTH stimulation test results.
Methods: Retrospective study (2008 – 2025). Dogs that had both a pheochromocytoma and a cortical tumor were excluded. A StimPos was defined as cortisol concentrations above laboratory cutoff, consistent with hypercortisolism. Frequencies were compared with a Fisher’s Exact test.
Results: The difference in frequency of StimPos was not significant when comparing adrenocortical tumors (31 of 70 [44%]) to pheochromocytomas (14 of 51 [27%]; p = 0.09) or adrenocortical adenomas (16 of 31 [51%]) to carcinomas (15 of 39 [38%]; p = 0.3). A Receiver Operating Characteristic (ROC) curve for post ACTH cortisol concentrations comparing medullary and cortical tumors yielded poor diagnostic value with an area under the curve (AUC) = 0.63 (95%CI 0.53 – 0.73; p = 0.01). Similarly, ROC curve comparing cortical adenomas vs. carcinomas yielded poor diagnostic value with an AUC = 0.51 (95%CI 0.37 – 0.65; p = 0.9). Conclusions and clinical importance: The ACTH stimulation test cannot predict adrenal tumor type in dogs.
