Comparison of methods to determine primary tumour size in canine apocrine gland anal sac adenocarcinoma

Objectives To assess agreement between measurement of primary apocrine gland anal sac adenocarcinoma tumours using digital palpation, computed tomography (CT) and formalin-fixed tissue and to look for associations with metastasis at presentation. Materials and Methods Retrospective study of different methods of measuring primary tumour size in histopathologically-confirmed canine apocrine gland anal sac adenocarcinoma. Results One hundred sixteen tumours from 107 dogs were included. There was moderate agreement between maximal dimension of the primary tumour measured by CT compared to formalin-fixed tissue and digital palpation, respectively. There was no significant difference in median maximum dimension between the measurement methods. Vascular invasion, CT stage, digital rectal examination stage and formalin-fixed tissue stage were significantly associated with metastasis at presentation, while mitotic index of the primary tumour was not. Dogs with tumours >2.5 cm (tumour-stage 2) were significantly more likely to present with metastatic disease. Clinical Significance In canine apocrine gland anal sac adenocarcinoma, primary tumour size, tumour-stage and vascular invasion are strong predictors of metastasis at presentation.