Anal sac gland carcinoma (also known as apocrine gland carcinoma of the anal sacs and anal sac adenocarcinoma) is a malignant tumour of the anal sacs of the dog. It is a relatively uncommon tumour but it is seen with increased frequency in English Cocker Spaniels in particular and other spaniels to a lesser degree.
Anal sac gland carcinoma
The anal sacs are 2 scent glands located either side of the anus in the dog. They are usually emptied when a motion is passed. In some dogs a tumour develops in the glandular tissue in the sacs. The fact that the disease is more common in some breeds of dogs suggests that genetic factors are involved but no one really knows for sure why some dogs develop the disease. In many cases this is the only site in which the tumour is growing but sometimes the tumour may spread to the lymph nodes or via the bloodstream to places like the lungs, liver and spleen.
A large proportion of these tumours are discovered by chance when a dog is presented for evacuation of the anal sacs. Sometimes the dogs develop irritation of the anal sacs which prompts this check in the first place, though this is unusual. In some cases owners actually see a swelling under the tail and next to the anus but it is rare for the tumour to grow big enough to cause problems at the original site.
You may notice changes in your pet that reflect spread of the tumour or are a consequence of substances produced by the tumour. Sometimes these tumours produce a hormone that causes excessive drinking and urination. This may be the only problem evident prior to diagnosis of the tumour.
Your vet may suspect the disease from examination of your pet and may be able to feel a swelling in the gland on rectal examination of your dog. In order to plan the most appropriate treatment, your vet will want to know the extent of the tumour. They will want to take samples if they suspect that the tumour has spread to the lymph nodes or to other organs. In addition they will want to take some blood tests and may need to check blood calcium levels as this is related to the hormone disturbance noted above.
The presence or absence of spread can be determined by X-rays and ultrasound examinations. These can usually be performed under light sedation.
There are a number of treatment options available for the management of anal sac gland carcinoma. Decisions are made on the basis of a number of factors, primarily whether and where the tumour has spread at diagnosis.
For patients with small (less than 3cm diameter) tumours and no evidence of spread of the tumour, surgical removal of the tumour is likely to be the most appropriate therapy. For patients where the tumour cannot be completely removed, radiotherapy can be used post-operatively to improve the tumour control.
For patients with larger primary tumours but still no evidence of spread, chemotherapy can be used to attempt to shrink the tumour, before surgery. This makes the surgery easier and may reduce the risk of post-operative complications. Again, radiotherapy may be appropriate following surgery to improve the duration of the resulting complete remission.
In some patients, where the tumour has spread to the lymph nodes but no further, the treatment plan is determined by whether or not those enlarged lymph nodes can be removed surgically. As always, the aim is to achieve optimal quality of life first and foremost and a good long life second. Therefore, if it is apparent that the enlarged lymph nodes can be removed without causing undue risk, they are removed.
If the lymph nodes look like they cannot be removed in their entirety or without presenting the patient with undue risk, they can be left or managed by either chemotherapy or radiotherapy or sometimes by a combination of these. Subsequent surgery can be performed in these dogs to remove other lymph nodes that become enlarged months or years in the future.
The average life expectancy for a dog with a small tumour that is removed by surgery is three years and three months. Dogs with larger tumours that have chemotherapy before surgery have an average life expectancy of two years.
For patients where the lymph nodes are involved but they can be removed there is an average life expectancy of sixteen months. If the lymph nodes cannot be removed then sadly less than 50% of these patients live more than 12 months from the time of diagnosis but as before, their quality of life is paramount during this time and measures are always being taken to ensure their well-being.
The final group of patients is the group with cancer that has spread throughout their body. Of course this is the worst case scenario but even in this situation patients can enjoy a normal quality of life for long periods of time with appropriate management.
Despite the gravity of a diagnosis of malignant cancer, some patients can enjoy an extremely prolonged period of complete normality and an excellent quality of life with appropriate therapy.