Immunohistochemical expression of CYP11A1, CYP11B, CYP17, and HSD3B2 in functional and nonfunctional canine adrenocortical tumors.

Background: Functionality of human adrenal tumors is inferred by CYP11B1 (cortisol synthase) expression, CYP11B2 (aldosterone synthase) expression, or both.

Hypothesis/objectives: Nonfunctional canine adrenal tumors have low expression of steroidogenic enzymes, whereas aldosterone-producing tumors express CYP11B, and cortisol-producing tumors express both CYP11B and CYP17.

Animals: Twenty-two client-owned dogs with adrenocortical tumors (ACT) (8 nonfunctional, 7-cortisol producing, 2 aldosterone-producing and 5 functional noncortisol producing) and 2 dogs with normal adrenal glands.

Methods: Retrospective case series. Adrenal functionality was determined from clinical signs and endocrine testing. CYP11A1, CYP11B, CYP17, and HSD3B2 expression was detected by immunohistochemistry on formalin-fixed paraffin-embedded adrenal tissue. Protein expression was semiquantified by 2 blinded observers using H-scoring (results reported as median [range]) and compared in nonfunctional and cortisol-producing adrenal tumors by Mann-Whitney U tests.

Results: CYP11A1, CYP11B, and HSD3B2 were present within all cortical layers of normal adrenal glands, and CYP17 was expressed within the zona fasciculata and zona reticularis. Expression of CYP11A1 (191.25 [97.5-270] vs. 175 [102.5-295] P = .69), CYP11B (190 [130-265] vs. 147.5 [95-202.5]; P = .07), CYP17 (177.5 [87.5-240] vs. 247.5 [55-292.5]; P = .40), and HSD3B2 (230 [47.5-295] vs. 277.5 [67.5-295]; P = .34) were not significantly different between cortisol-producing and nonfunctional ACT.

Conclusions and clinical importance: Our findings suggest it is not possible to determine functionality of canine ACT by immunohistochemistry for steroidogenic enzymes. Tumor size cannot be used to infer functionality of adrenal tumors.