The Utrecht Score: A novel histopathological scoring system to assess the prognosis of dogs with cortisol‐secreting adrenocortical tumours

A cortisol‐secreting adrenocortical tumour (ACT) is the cause of naturally occurring canine hypercortisolism in approximately 15% to 20% of cases. The differentiation between an adrenocortical adenoma and carcinoma is usually based on histopathology. However, histopathological parameters have never been linked to the dogs' survival. Moreover, in human medicine the inter‐observer variability of some histopathological parameters that are used for ACTs is high. The objective of this study was to establish a reliable and easy‐to‐use histopathological scoring system for cortisol‐secreting ACTs that can assess the prognosis of dogs after adrenalectomy. Cortisol‐secreting ACTs of 50 dogs, collected between 2002 and 2015, were included in this study. Twenty histopathological features were assessed by one veterinary pathologist and one resident in veterinary pathology. In addition, the Ki67 proliferation index was assessed by two observers. Only parameters with intra‐ and inter‐observer agreement scores (intra‐class correlation or Cohen's kappa coefficient) of ≥0.40 were included in survival analyses. Use of multivariate forward stepwise regression analysis with associated hazard ratios led us to a scoring system which we call the Utrecht score: the Ki67 proliferation index, +4 if more than 33% of the tumour cells have clear/vacuolated cytoplasm and + 3 if necrosis is present. Using cut‐off values of 6 and 11, we could distinguish three groups that had significantly shorter survival times with increasing Utrecht scores. We conclude that the Utrecht score can be used to assess the prognosis of dogs with cortisol‐secreting ACTs after adrenalectomy, which can help to select high‐risk dogs that might benefit from adjuvant treatment or additional monitoring.