The Dog Cancer Survival Guide (116 page)

Other tumors can develop in the anal region, including squamous cell carcinoma in the lining of the anal sacs, lymphoma, mast cell tumors, skin melanoma, soft tissue sarcomas and transmissible venereal tumors (some of these are discussed in other chapters).

We used to think that females were more prone to anal sac adenocarcinoma than males; recently, reports show both males and females are equally affected.

Perianal tumors are one of the most common tumors in dogs, especially intact male dogs. Because testosterone influences the development of normal perianal glands and perianal tumors, neutering in early life can prevent perianal adenomas. Females that develop these tumors are typically spayed, and may have elevated testosterone levels, due to an adrenal tumor. There is also an association, in dogs, with testosterone-secreting testicular tumors.

Certain breeds are more prone to anal tumors than others. Those most likely to get perianal adenomas (benign tumors) are the arctic breeds such as Alaskan Malamutes, Siberian Huskies, Samoyeds and Norwegian Elkhounds. Other breeds predisposed to perianal adenomas are the Beagle, Cocker Spaniel, Shih Tzu and English Bulldog.

The more aggressive perianal adenocarcinoma shows up more often in large breeds, including German Shepherds and the arctic breeds: Alaskan Malamutes, Siberian Huskies, Samoyeds and Norwegian Elkhounds.

The following breeds are more likely to develop anal sac adenocarcinoma: Cocker Spaniels, English Springer Spaniels, German Shepherds and Golden Retrievers.

Vets find about one-third of the aggressive anal sac adenocarcinomas during a routine physical examination, which is why I urge you to request a rectal exam. A rectal exam can evaluate not only the anal sacs, but also lymph nodes and other glands in the anal region. This is important, because many times the primary tumor in the anal sac is very small, and there is much more extensive metastasis to the regional lymph nodes in the pelvic canal and under the lumbar spine, which may be palpable on an exam. A rectal exam can also reveal benign perianal adenomas.

If the tumor is not caught during a routine exam, owners often notice the mass itself swelling from underneath the tail. If the mass is not visible on the surface, the dog may show other symptoms, including straining to defecate, swelling in the area, licking or biting the region, or scooting along the ground in an attempt to relieve the associated itching or pain (or both).

Benign perianal adenomas usually develop over months or even years, and are mostly limited to one mass (although they can come in multiples).

Both perianal and anal sac adenocarcinomas grow more quickly, and these malignancies are more fixed (more attached to underlying tissues) and more likely to be ulcerated (open, raw, bleeding). If your dog is a female or a neutered male, the malignant perianal adenocarcinoma is more likely to occur than the benign perianal form.

Depending upon which study you look at, about 25-50% of dogs with anal sac adenocarcinoma have increased blood calcium levels at the time of diagnosis. These dogs may be drinking and urinating more often, vomiting, be physically weak and reluctant to eat or feel depressed.

A fine needle aspirate of the mass can usually help the vet to distinguish whether the tumor is an abscess (infection), a benign adenoma or a malignant carcinoma. The aspirate rarely requires sedation, and is an easy and quick test to run. The vet or the cytologist at the lab will be able to tell what the mass is by looking at the cells under a microscope, and the malignancies are typically easy to tell from the benign tumors. Benign perianal adenomas contain cells shaped like liver cells, which is why they are often called “hepatoid” tumors (hepatocytes are liver cells).

If a carcinoma is confirmed by the aspirate, a surgery can be planned with a wide excision and submitted for biopsy to look at its margins. If the margins are not wide, a second surgery or radiation therapy may be recommended to prevent recurrence. (Wide margins are ideally two to three centimeters, but the location or size of the tumor may not allow for this. In most cases, we can get one to two centimeter margins in these tumors.)

If a malignancy is suspected, additional testing should be done before attempting a curative treatment. Urinalysis and blood work are recommended to get a general picture of the overall health of your dog. One of the important factors to look at on the blood panel is the calcium levels.

“Be truly open-minded about alternative therapies. We used both traditional (radiation) and alternative (supplements, immune support etc.) at the same time. If I had it to do over again, I would have tried the alternatives first, and only done traditional if necessary. I think the traditional therapies really strained our twelve-year-old golden - I wish I had trusted the alternatives enough to really give them a go first.”

-
Sheryl Poole, Andover, Massachusetts

About 25-50% of dogs with anal sac adenocarcinoma have increased blood calcium levels at the time of diagnosis, because ASAC tumors produce PTHrp (parathyroid hormone-related peptide), a protein that causes blood calcium levels to rise. This marker is an indication that the tumor is particularly aggressive and requires prompt management. Dogs with elevated blood calcium have a worse prognosis.

One of the most common causes of elevated blood calcium is ASAC, but other diseases can also cause this condition. Lymphoma is the other most common cancer cause, followed by other non-cancer causes, such as kidney disease, Addison’s disease, diseases that break down the bones such as hyperparathyroidism and vitamin D toxicity. Simple lab error can also be the culprit. All of these must be ruled out to make sure the elevated levels are associated with ASAC, and help you make treatment plans.

To confirm elevated blood calcium levels, a test that measures
ionized
calcium levels should be run. (Most chemistry panels measure total calcium, not ionized calcium.) This measures the active form, and if the levels are elevated, it’s a sign that ASAC is the culprit. Even if total calcium levels are normal, check the ionized form, because knowing this number can be predictive for your dog’s outcome. Your dog may need oral medications to lower these levels.

Metastasis occurs early in ASAC development, which is why looking for metastasis up front is important. More than 50% of dogs already have spread at the time of diagnosis. Up to 90% of these dogs will have regional lymph node metastasis, often in their sublumbar (under the lumbar spine) and intrapelvic (inside the pelvis) nodes. Metastasis can also spread to the liver, spleen, lungs and bone, so chest X-rays and abdominal ultrasounds should be run to check these areas for suspicious lesions. If your dog is lame, regional X-rays should also be taken.

Perianal ACA is less aggressive in general, although 15% of dogs will have metastasis at the time of diagnosis, making checking for spread important. The same locations and tests are recommended as for ASAC.

Here is the most recent staging system for these tumors published by Polton in 2007 for ASAC:

• Stage 1:
  The primary tumor is smaller than or equal to 2.5 centimeter in diameter, with no regional lymph node or distant metastasis.
  
• Stage 2:
  The primary tumor is greater than 2.5 centimeter in diameter, with no regional or distant metastasis.
  
• Stage 3A:
  The primary tumor is of any size, but there is regional lymph node involvement with tumors smaller than or equal to 4.5 centimeter in diameter, with no distant metastasis.
  
• Stage 3B:
  The primary tumor is of any size, but there is regional lymph node involvement with tumors greater than 4.5 centimeter in diameter, with no distant metastasis.
  
• Stage 4:
  The primary tumor is of any size, with or without lymph node involvement, and distant metastasis is present.
  

In general, the higher the stage is, the worse the prognosis. In general, the prognosis worsens when the primary tumor is large, when there is lymph node metastasis, when there is distant metastasis or an increase in ionized calcium levels.

The median survival time for dogs that have anal sac adenocarcinomas and are not treated is about eight months.

However, it’s been shown that these tumors are truly variable from dog to dog. For example, one study looked at eleven dogs who did not receive treatment for their anal sac ACA, five of whom had bulky regional metastasis when they were diagnosed, and three of whom had both regional and lung metastasis. The median survival time for the group was about eight months, and the range of survival times was 0 days to 499 days (about sixteen months). While there were not many dogs in this study, it does illustrate that it’s hard to say that these tumors have a “typical” behavior.

With full treatment (surgery, chemotherapy and radiation) as described below, studies show that dogs with anal sac adenocarcinoma have survival times approaching two to two and a half years.

With treatment for perianal ACA, the size of the primary tumor is very predictive of prognosis. Dogs with tumors smaller than 5 centimeters have a median survival time of two years, while those with tumors larger than 5 centimeter have a survival time of one year. Dogs with metastasis at time of diagnosis experience a median survival time of seven months.

The vast majority (90%) of perianal adenomas are cured completely with castration and surgical removal of the tumor.

Surgery is the first treatment for all perianal tumors, and may be the only treatment needed, depending upon the tumor type and the extent of the disease.

Perianal adenomas often resolve themselves when your dog is neutered, because the source of testosterone is removed with the surgery. Those that don’t go away or shrink significantly can be surgically removed. Over 90% of these tumors will be cured with castration and tumor resection.