SOX9 and Ki67 as novel prognostic factors in canine corticotroph pituitary tumors

Abstract

Background Pituitary-dependent hypercortisolism (PDH) is a common endocrinological disorder in dogs. This disorder is caused by an adrenocorticotropic hormone (ACTH)-secreting adenoma in the pituitary gland. Transsphenoidal hypophysectomy has shown to be an effective treatment for PDH, for which the pituitary height/brain area ratio (P/B ratio) is an important prognostic marker. Additional prognostic biomarkers could help to select dogs that could benefit from additional treatment or monitoring after surgery. The objective of this study was to investigate the prognostic value of stem cell marker sex determining region Y-box (SOX9) and proliferation marker Ki67 in canine corticotroph pituitary adenomas.

Method Protein expression of SOX9 and Ki67 was analyzed by immunohistochemical stainings in 31 enlarged corticotroph pituitary adenomas of dogs that underwent hypophysectomy between 2015 and 2021. For SOX9 quantification, the H-score was assessed twice by visual scoring with a light microscope. The Ki67 proliferation index (PI) was determined by calculating the percentage of positive nuclei in at least 1000 cells in a hotspot area per tumor slide. Statistical analyses was performed to determine the correlations between the P/B ratio, SOX9 and Ki67. To assess the effect of the prognostic factors on the disease-free survival time, univariate and multivariate survival analyses were performed using the Cox proportional hazards model. The Kaplan-Meier limit-method was used to compare disease-free survival times between groups.

Results The P/B ratio and Ki67 PI were both significantly associated with survival in univariate survival analyses, and were correlated with each other. The H-score of SOX9 showed a trend towards being significantly associated with poor prognosis after surgery in univariate analysis. Dogs with corticotroph pituitary adenomas that had high SOX9 H-scores or high Ki67 PI’s had worse disease-free survival times than those with low scores. The multivariate regression model with forward selection showed that the Ki67 PI and SOX9 H-score were independent prognostic factors for dogs with PDH after hypophysectomy.

Conclusion This research provided evidence that stem cell marker SOX9 and proliferation marker Ki67 are useful intra-tumoral predictors of recurrence of PDH for dogs after hypophysectomy. These novel prognostic factors are promising markers that can be used to select dogs that would benefit from additional monitoring and/or adjuvant therapy.