Dogs have small pouches, called anal sacs, located on either side of their anal opening. These sacs can become inflamed, infected or blocked and may cause dogs to “scoot” their bottoms on the ground or lick and chew the area for relief.
Tumours of the anal sac are called apocrine gland adenocarcinoma and although uncommon, are very serious. This type of cancer usually affects older dogs (10 years on) and is more common in spaniel breeds and others including German Shorthair Pointers, Dachshunds and Alaskan Malamutes.
Apocrine gland adenocarcinoma tends to spread in the early stages of the disease to surrounding tissue and local lymph nodes even if the tumour is small. Often, this type of cancer has already spread at the time of diagnosis, making successful treatment more difficult.
In later stages of the disease, apocrine gland adenocarcinoma tends to spread to the lungs, spleen, liver, kidneys and/or lumbar vertebrae. In about 25 per cent of cases, the tumour causes elevated blood calcium (hypercalcemia), which can cause kidney failure.
Early detection of apocrine gland adenocarcinoma can greatly improve survival time so it’s important to take your dog to the vet at least once a year and ask your vet to make a rectal exam part of your dog’s check up.
The cause of apocrine gland adenocarcinoma is unknown. This type of cancer is common in dogs, but not in cats and may be associated with a hormone imbalance in the body.
Other symptoms in dogs with elevated calcium levels (found in 25% of dogs with apocrine gland adenocarcinoma) may include excessive thirst, increased urination, vomiting, loss of appetite and lethargy.
If your dog is suspected of having apocrine gland adenocarcinoma, your vet will conduct a number of tests to reach a definitive diagnosis and to determine whether the cancer has spread and to what extent.
Blood tests will give your vet a good overall picture of your dog’s health and help determine kidney function and whether or not your dog has elevated calcium levels. A small needle is inserted into the tumour (aspiration) to get a cell sample, which helps determine the presence of a tumour and rule out other conditions such as infection and/or inflammation.
Because this type of cancer tends to spread quickly, chest x-rays will reveal if the cancer has spread to the lungs and/or heart and an abdominal ultrasound will determine if the cancer has spread to the lymph nodes or other organs such as the liver and kidneys.
Treatment for apocrine gland adenocarcinoma usually involves surgery along with chemotherapy and/or radiation therapy. Successful treatment depends on a number of things including tumour size, presence of hypercalcemia (elevated calcium levels) and the extent to which the cancer has spread.
The tumour can often be surgically removed but because of its location, the vet may not be able to remove a wide margin around the tumour without the risk of serious surgical complications such as the incision breaking open and not healing properly, incontinence and infection.
In about half of all apocrine gland adenocarcinoma cases, dogs will have enlarged lymph nodes in the abdomen. Removing the enlarged lymph nodes, during tumour removal or after, will usually help alleviate constipation and difficulty defecating.
If the dog has elevated calcium levels in the blood, which can cause kidney failure, treatment may be necessary before surgery so the dog can better tolerate the anaesthetic.
After surgery, chemotherapy and/or radiation therapy may help improve survival times. Radiation therapy can be used alone to control tumour growth or on dogs where surgery is not an option.
Vets estimate the survival time for dogs treated with surgery alone is about six months to a year. If surgery is combined with chemotherapy and/or radiation therapy, survival times may increase to 18 months for dogs with a small tumour (less than 10 cm). For dogs with apocrine gland adenocarcinoma and hypercalcemia, the survival time is cut in half to about nine months.
This page has been reviewed by our Panel of Experts for accuracy. Our Panel of Experts is comprised of practitioners with varying specialties and perspectives. As such, the views expressed here may not be shared by all members of our Panel.
The content on this website is for informational purposes only and is not intended to be a substitute for professional veterinary medical advice, diagnosis or treatment.
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