Cancer in dogs
One of the most common routine procedures I perform at the Manchester Animal Hospital is expressing the anal glands. Anal glands are basically small balloons filled with a brown liquid notorious for its repulsively metallic, fishy smell.
Dogs have two anal glands that sit just inside their anus at the 4 and 8 o’clock positions. When the dog defecates, some of the stinky fluid in these sacs is squeezed out with the feces. This liquid may play a role in territorial marking and communication amongst dogs.
There are many problems that can affect a dog’s anal sacs, including tumors. Anal sac tumors are abnormal, usually cancerous growths in the anal sac. They are uncommon but serious and left untreated are generally fatal. They can affect any dog but older dogs and certain breeds such as Spaniels, German Shepherds, and Dachshunds are at higher risk. These tumors cause problems as they spread locally and to distant sites of the body in a process called metastasis. They can bring illness, discomfort and a decreased quality of life to your dog. Thus, it is essential to catch these tumors early and to treat them as soon as possible.
As with most cancers, a cause has not been identified. However, genetics and environmental factors probably play important roles. Although I can’t pinpoint a cause, I do have some understanding of what’s happening at a microscopic level. For whatever reason, cells in the anal sac start dividing and multiplying in an uncontrolled manner. This cell division creates a mass that is usually cancerous. The mass makes the anal sac larger, but this alone usually doesn’t cause issues, at least until the mass gets quite large. The big problem is when cancer cells break away and travel to other parts of the body to make new tumors. The cells often spread to lymph nodes, which are small lumps of immune tissue scattered throughout the body. They can also spread to essential organs, such as the lungs, liver and kidneys
The signs and symptoms depend on the behavior of the tumor and where it has spread. Many dogs won’t show any signs. However, when the tumor spreads to nearby lymph nodes or the mass gets large, your dog may strain and struggle to defecate, or not even defecate at all. They can also have ribbon-like stool and swollen back legs. When the tumor increases blood calcium levels, your dog may drink and pee more, eat less, vomit and seem weak and tired. Other possible signs include, swelling at the rear end, licking the rear end more than usual, bleeding around the anus and bloody stool.
Dogs with anal sac tumors may also scoot, meaning they sit and drag their rear end against the ground. However, scooting much more commonly indicates full or inflamed anal glands that need to be expressed (squeezed) rather than cancer.
Until more serious treatment can be pursued, I might recommend stool softeners to make it easier for your dog to defecate and give fluids and medications to lower blood calcium. I perform the surgery required unless I feel a referral to a veterinary surgeon is required if the tumor has advanced. If it is possible, treatment generally involves surgical removal of the mass and any enlarged lymph nodes in the area. Surgery has been shown to lengthen the survival time of dogs with anal sac tumors. However, tumors may eventually reappear if cancer cells are left behind and the cancer cells may have already spread to other sites at the time of removal. After surgery, some dogs won’t be able to control their bowel movements for a while and there is a risk the surgical site, especially it is near the route feces take out of the body.
Because anal sac tumors have such a high risk of spread, chemotherapy is often recommended after surgery. It involves giving medications, often via the mouth or blood, to kill or inhibit cancer cells throughout the body.
Dogs who receive surgery or any type of treatment generally have a better prognosis whereas the outlook is often less promising for dogs with larger tumors, high blood calcium levels, and extensive spread of the tumor.
There’s no proven way to prevent anal sac tumors from developing. Early detection is important and may be achieved through routine rectal exams performed by your veterinarian. In fact, sometimes anal sac tumors are an incidental finding during a seemingly healthy pet’s physical exam.
Dr. Lamb is the Veterinarian at the Manchester Animal Hospital.
