VETcpd - Oncology Peer Reviewed Canine anal sac adenocarcinoma – a review

Anal sac adenocarcinoma is the most common malignant arising from canine anal sacs. , particularly to the local lymph nodes, is a relatively frequent feature of the disease and paraneoplastic can result. Thorough staging is therefore indicated once a diagnosis of anal sac adenocarcinoma has been made. Surgical excision of the affected anal sac is the treatment of choice for the primary tumour and concurrent lymphadenectomy Julia Riggs is advocated where regional nodal metastasis has occurred. and MA VetMB AFHEA DipECVS MRCVS radiotherapy may also be used alongside or instead of surgery to help manage EBVS European Specialist in the disease. Unfortunately, the majority of dogs with a diagnosis of anal sac Small Animal Surgery adenocarcinoma will develop progressive disease in spite of treatment and therefore RCVS Specialist in repeat staging is usually recommended. Small Animal Surgery By incorporating evidence from the recent veterinary literature, this article will review Having completed a surgical residency at the diagnostic and therapeutic options for canine anal sac adenocarcinoma and the University of Cambridge and passed outline the prognosis for dogs affected by this disease. the certifying examinations, Julia became Key words: Anal sac, anal sac adenocarcinoma, apocrine gland a European Specialist in Small Animal adenocarcinoma, anal sacculectomy Surgery in 2018. She subsequently spent two years working as a Soft Tissue Surgeon in a private referral practice Introduction before returning to work in the Soft Anal sac adenocarcinoma is a highly Barnes and Demetriou 2017; Skorupski Tissue Surgery team at the University of malignant neoplasm arising from the et al. 2018; Elliott 2019). Sex distribution Cambridge in 2019. apocrine glands of canine anal sacs. It appears to be approximately equal E: [email protected] is by far the most common malignant (Williams et al. 2003; Potanas et al. 2015). tumour to affect these structures, though Despite its malignant behaviour, a wide malignant melanoma (Vinayak et al. 2017) range of treatments for primary, metastatic and squamous cell carcinoma (Esplin et and recurrent anal sac adenocarcinoma al. 2003; Mellett et al. 2015; Giuliano lesions are available. These have led to et al. 2017) have also been reported. improved survival times for affected Anal sac adenocarcinoma will frequently dogs, though ultimately most dogs will metastasise to the local iliosacral lymph unfortunately still succumb to the disease. node chain; rarely distant metastasis to the liver, spleen, , bone and spinal Diagnosis Clinical signs of anal sac adenocarcinoma cord can also occur (Bennett et al. may or may not be apparent in affected 2002; Meuten et al. 1981; Brisson et al. dogs. When clinical signs are present they 2004; Giuliano et al. 2015). Parathyroid tend to result from metastatic disease hormone-related protein (PTHrP) may be and/or paraneoplastic hypercalcaemia, secreted by the neoplastic cells resulting rather than the anal sac mass itself. Anal in pseudohyperparathyroidism (Rosol sac masses only cause visible perineal et al. 1990). Increased osteoclast activity, swelling when they have reached an increased gastrointestinal absorption appreciable size; small masses are therefore and decreased renal excretion result in more commonly detected incidentally hypercalcaemia (and hypophosphataemia), upon routine rectal palpation (Figure 1). though clinical signs of this are not Iliosacral lymphadenomegaly can cause always observed. Whilst any age and tenesmus, dyschezia, altered stool shape, breed of dog can be affected by anal sac constipation and obstipation as progressive SUBSCRIBE TO VETCPD JOURNAL adenocarcinoma, older dogs (median of pelvic canal obstruction occurs (Bennett 9-11 years) and spaniels (especially the et al. 2002). Dogs with concurrent Call us on 01225 445561 English cocker spaniel) appear over- hypercalcaemia of malignancy may or visit www.vetcpd.co.uk represented (Bennett et al. 2002; Williams show polydipsia and polyuria, weakness, et al. 2003; Polton and Brearley 2007; anorexia, vomiting and constipation.

Page 20 - VETcpd - Vol 7 - Issue 3 VETcpd - Oncology

Staging Once a presumptive or definitive diagnosis of anal sac adenocarcinoma has been made, thorough staging is recommended to ascertain whether metastatic and/or paraneoplastic disease is present and to guide subsequent therapeutic decision-making. The TNM classification system (as described for epidermal and dermal tumours by the World Health Organisation) applies to anal sac adenocarcinoma staging, however Figure 2: Characteristic fine needle aspirate cytology a modified staging system specific to of canine anal sac adenocarcinoma. Clustered this tumour type has also been described epithelial cells (arrow) are present amongst a (Owen 1980; Polton and Brearley 2007). background of red blood cells. Cytoplasmic borders are indistinct, which is a typical cytological feature of Comprehensive serum biochemistry Figure 1: A left-sided, unilateral anal sac mass causing these tumours. Despite their aggressive behaviour, and a complete blood count should perineal swelling. The dog has been clipped ahead of the epithelial cells do not possess many criteria of be performed in all dogs, with specific surgical excision. malignancy on cytology attention being paid to the calcium level and renal parameters. Hypercalcaemia of Figure 3: malignancy has been documented to occur Ultrasonographic appearance of an in approximately one third to half of dogs enlarged left medial diagnosed with anal sac adenocarcinoma iliac in a and azotaemia may develop due to renal dog with metastatic tubular damage (Bennett et al. 2002; anal sac adenocarcinoma. The lymph node has Williams et al. 2003). Although not an irregular profile with routinely performed in the work-up diffuse heterogenous of dogs with anal sac adenocarcinoma, echogenicity; it measures parathyroid hormone (PTH) and PTHrP 4 x 1.3cm. can be measured alongside calcium in blood tests; in a dog with hypercalcaemia of malignancy a low PTH and high PTHrP would be expected. Urinalysis, preferably of a cystocentesis sample, should be performed to further evaluate renal function and screen for urinary tract infection (to which hypercalcaemic patients are predisposed). However, some dogs with hypercalcaemia Fine needle aspiration of an anal sac Metastasis is reported in more than may not show any associated clinical mass will frequently allow a presumptive half of dogs diagnosed with anal sac signs depending on their overall calcium diagnosis of anal sac adenocarcinoma adenocarcinoma (Bennett et al. 2002; concentration and the rate at which the to be made. This may be possible in the Polton and Brearley 2007). Most level has increased. conscious patient if a large mass is present, commonly the iliosacral (medial iliac, Careful rectal examination should be though sedation is recommended for internal iliac and sacral) lymph nodes performed in any dog with suspected anal fractious animals, those in discomfort or are affected, although spread to other sac adenocarcinoma. Whilst uncommon, when the mass is small. Rectal palpation organs can also occur. Whilst pulmonary bilateral anal sac masses can occur using the non-dominant hand may metastasis is not a frequent feature of (Goldschmidt and Zoltowski 1981; Emms help stabilise a small anal sac mass and the disease, the effect of this on overall 2005; Potanas et al. 2015) and therefore guide the collection of aspirates by the prognosis means that thoracic imaging both sacs should be felt. Dogs with a dominant hand. Cytological features of by orthogonal view or history of anal sacculitis or impaction adenocarcinoma aspirates include clusters computed tomography (CT) is usually may have residual aggregates of secretion of cuboidal epithelial cells with indistinct recommended. Options for imaging the within the sac lumen and thickened anal cytoplasmic borders, light blue cytoplasm abdominal cavity include ultrasonography, sac walls – palpation under sedation may and round nuclei (Figure 2). The cells may CT and magnetic resonance imaging facilitate sac expression in such cases. show an acinar arrangement. Despite the (MRI). MRI and CT have been shown Non-expressible masses remaining after aggressive clinical behaviour of anal sac to be more sensitive than ultrasonography successful evacuation of sac contents adenocarcinoma, the epithelial cells often in detecting iliosacral lymphadenopathy, should raise the suspicion for malignancy. lack criteria of malignancy on cytology. however ultrasonography still remains the Rectal examination may also reveal Incisional biopsies and histopathology most commonly used imaging modality sacral lymph node enlargement dorsal can also be performed to gain a more in the clinical setting (Llabrés-Díaz or dorsolateral to the rectum within the definitive diagnosis of an anal sac mass, 2004; Anderson et al. 2015; Palladino et pelvic canal. though this step is often not required. al. 2016) (Figure 3). Enlarged lymph

VETcpd - Vol 7 Issue 3 - Page 21