What is an anal sac gland tumor?
This tumor is a disordered and purposeless overgrowth of cells originating from the modified sweat glands of an anal sac. There are a pair of anal sacs, one each side of the anus between the external and internal anal sphincter. The glands normally produce bad-smelling grey-brown granular secretions. The tumor is usually rapidly growing, almost always malignant (spreading), and extends deep into surrounding tissues. There can be abnormal hormone production by the tumor cells and these hormones can cause widespread physiological effects in the animal. The malignant tumor (anal gland carcinoma) may also spread to other parts of the body (metastasize), but such metastasis is usually slow to occur.
What do we know about the cause?
The reason why a particular dog may develop this, or any cancer, is not straightforward. Cancer is often seemingly the culmination of a series of circumstances that come together for the unfortunate individual.
We do not know what causes this tumor.
Is this a common tumor?
No. The malignant form of the tumor (carcinoma) is uncommon in dogs. Benign (non-invasive) forms of this tumor are almost unknown.
How will this cancer affect my dog?
The tumors may be noticed as a lump beside the anus but growth is often inwards so the lump may not appear as large as the actual tumor. Anal sac dimension and the color and consistency of its content are highly variable so give no indication of the problem. The first signs may therefore be due to physical effects on the surrounding structures such as straining and difficulty in passing feces.
A large number of dogs with an anal sac tumor develop other clinical signs that are not readily explained by the local or wider spread of the tumor. This is known as a paraneoplastic syndrome. There is abnormal parathyroid hormone production by the cancer that induces increased drinking, increased urine production, muscle weakness, slow heart beat and increased calcium levels in the blood. Kidney failure is possible.
How is the tumor diagnosed?
Clinically, this tumor can be difficult to diagnose but the site is one indicator of the possible type. Accurate diagnosis relies upon microscopic examination of tissue. Cytology (the microscopic examination of cell samples drawn from the tumor using a needle and syringe) is sometimes helpful as a rapid or preliminary test. But histopathology (the microscopic examination of specially prepared and stained tissue sections made from actual pieces of the tumor) is needed for full diagnosis. This is done at a specialized laboratory where the slides are examined by a veterinary pathologist. The information from histopathology is more detailed than cytology and will better indicate how the cancer will behave (the prognosis) and whether the cancer has been fully removed.
What treatment is available?
Local treatment is surgical removal of as much of the cancer as possible given that it tends to be so invasive of surrounding tissues. However surgery may need to be repeated. Drug treatment (chemotherapy) or radiation may also be considered in some situations as a means of slowing recurrence or spread of the cancer.
Can this cancer disappear without treatment?
Essentially, the answer is ’No’.
How can I nurse my dog?
Preventing your pet from rubbing, scratching, licking or biting the tumor will reduce itching, inflammation, ulceration, infection and bleeding. Any ulcerated area needs to be kept clean.
After surgery, the operation site similarly needs to be kept clean and your pet should not be allowed to interfere with the site. Any loss of sutures or significant swelling or bleeding should be reported to your veterinarian.
You may be asked to check that your pet can pass urine and feces or to give treatment to facilitate this..
How will I know if the cancer is permanently cured?
’Cured’ has to be a guarded term in dealing with any cancer.
Histopathology will give your veterinarian the information that will help to indicate how the tumor is likely to behave. The veterinary pathologist usually adds a prognosis that indicates the probability of local recurrence or metastasis (distant spread). Other diagnostic tests such as radiographs of the chest and abdomen, and/or ultrasound of the abdomen may help determine if the cancer has already spread.
These tumors are almost always malignant and may already have spread to regional lymph nodes and then to various internal organs by the time the initial diagnosis is made. Even those that have not yet spread are usually not permanently cured and can recur. Another problem is hypercalcemia (high blood calcium), which often persists with kidney failure as a possible sequel.
The post-surgical survival range is two weeks to thirty-nine months (average eight months). Early detection and radical surgical removal of the lump and surrounding tissue gives a better prognosis but spread (metastasis) may have already occurred.
Are there any risks to my family or other pets?
No, this is not an infectious tumor and it is not transmitted from pet to pet or from pets to people.
Based on material written by Joan Rest, BVSc, PhD, MRCPath, MRCVS. and modified with permission from Lifelearn Inc. © Copyright 2004 Lifelearn Inc.
