Anal Sac Adenocarcinoma; A Hidden Cancer

Tumours of the perianal region occur frequently in dogs (Bennett et al. 2002), with benign adenomas comprising 5896% of tumours at this site (Turek & Withrow 2013). In some cases these may transform to become malignant perianal adenocarcinomas, and these need to be distinguished from adenocarcinomas which derive from the apocrine secretory epithelium within the wall of the anal sacs (Polton & Brearley 2007). Neoplasia of the squamous epithelial lining of the anal sac is uncommon (Polton et al. 2006; Mellett et al. 2014). Anal gland/sac adenocarcinomas (ASA) represent 2% of all skin and subcutaneous tumours in dogs, and around 17% of all perianal malignancies (Bennett et al. 2002; Turek & Withrow 2013; Potanas et al. 2015). They are clinically important because of their high metastatic potential and association with paraneoplastic hypercalcaemia; this review will therefore focus on this tumour type (Polton et al. 2006.; Wouda et al. 2013).