Anal Sac Adenocarcinoma in Dogs

Information for Pet Owners

Anal sac adenocarcinomas are most common in spaniel breeds, particularly English Cocker Spaniels. They occur under the tail adjacent to the anus and generally appear as a lump or swelling. Other tumours and infections can also occur in this area and a fine needle aspirate or surgical biopsy is required for diagnosis.

Approximately 50% of dogs diagnosed with anal sac adenocarcinoma will have spread of the tumour to other parts of the body at the time of diagnosis. Spread of the tumour is usually to the lymph nodes that sit in the 'sublumbar' area and your vet can check these by rectal examination combined with ultrasound or CT. The disease can also spread to other organs such as the lungs, liver and spleen and these can be checked by ultrasound and X-rays or by CT scan. Although anal sac adenocarcinomas commonly spread to other parts of the body they can progress relatively slowly from there and some dogs will live quite a long time despite metastasis.

Approximately 25-30% of dogs with anal sac adenocarcinoma will have tumours that cause calcium levels in the body to rise. The most common signs that you may notice if your dog is hypercalcemic are increased thirst and increased urination. If the anal sac adenocarcinoma can be controlled with treatment the hypercalcemia will resolve. The greatest risk of prolonged hypercalcemia is kidney damage and your vet can try a number of different treatments to reduce the likelihood of this occuring.

Depending on the results of X-rays, ultrasound or CT, surgery may be recommended for your dog to remove the primary tumour +/- the sublumbar lymph nodes. Most dogs then receive chemotherapy and some may also receive radiation therapy. Chemotherapy can be given by tablets or injection. It is well tolerated by dogs and quality of life is generally excellent. For more information on chemotherapy click here. For further information specific to your pet ask your vet to contact us for detailed advice.