Tumors of last inch of the GI Tract

There is not much written about the tumors that appear in the very last inch of the GI tract in pets. Each sex has its own syndrome. Anal tumors are rare in cats. Intact male dogs develop tumors of the tiny perianal glands that surround the anus. Senior female dogs develop malignancies of the anal sacs, some of which manifest hypercalcemia(abnormally large amounts of calcium in the bones).
 
Perianal Tumors in Intact Male Dogs
 
Perianal tumors in male dogs are considered benign and hormone dependant. They are expected to regress after castration; however, there is a subset, which will recur.
 
The larger tumors, over 0.5 cm, should be excised and submitted for biopsy to be determine or treated with cryotherapy while the dog is under anesthesia for castration. The recurrence rate for these tumors is about 50% after removing the stimulus of testosterone.
 
If recurrence prevails, the tumors should be excised and biopsied completely to evaluate the basement membrane of the gland to see if there is malignant activity. There may be other sources of male hormones such as the adrenal glands, which may contribute to the recurrence.
 
Some doctors have placed dogs on antiandrogen therapy. One could consider using Ketoconizole or Proscar for this purpose. Other drugs with activity in this area are available in England and Canada. I recall using one drug with the trade name “Ticar” which was helpful for a few patients while supplies lasted.
 
Malignant Anal Tumors In Male Dogs

The typical history of malignant anal tumors in male dogs are that, half of the cases are initially presented to their local veterinarian with one large perianal mass. The other half of anal tumors were discovered by their local vet on a routine physical exam, or when the pet was presented for another reason.
 
Some dogs were presented with several nodules around the anus involving the sphincter muscles. Some of the tumors may have been infected, ulcerated and cause the dog to worry the area with persistent licking and chewing of the site. Generally, the dog had one or two excisional biopsy procedures prior to the metastatic event, which led them to our service.
 
In most causes, the length of time a mumor can metastasize was at least several months and often 9-12 months following the first or second surgery.  Follow up visits with rectal palpation were variable. Dogs generally presented with a history of tenesmus (urination defect) and or constipation problems, may have a history of abnormal eliminations with ribbon-like stool or smaller than normal size or droppings from one angle. Local recurrence was often accompanied by the presence of a large sub-lumbar mass obstructing the distal colon.
 
Some dogs present with deep sphincter recurrence along with the sub-lumbar lymphadenopathy (situated under swollen lymph nodes) 6 to 9 months post initial surgery. Panels on these dogs do not show abnormalities in calcium levels.
 
Most of the dogs were suspected to have routine perianal tumors and there is no way to tell the malignant tumors apart from the benign ones, unless they are biopsied.
 
The end result to consider is that 50% recur after attempts to control them by castration and dogs die of metastases to the sub-lumbar lymph nodes.  With these events in mind, it is recommended that a more analytical approach and a more rigid follow-up program to scout for recurrent perianal tumors in senior male dogs.
 
Anal Sac Carcinomas of Female Dogs

Hypercalcemia is a tell tale marker for anal sac carcinoma in female dogs. If the dog does not exhibit the enlarged lymph nodes, which are characteristic of lymphoma, a search for anal sac carcinoma is indicated.   Anal sac carcinomas should be considered very aggressive from the start. Even small tumors release cancer cells that travel forward involving the dorsal rectal nodes, the sub-lumbar and iliac lymph node chain.
 
Symptoms typical of hypercalcemia are increased thirst and urine output (polydypsia and polyuria). Renal injury is an abnormal condition resulting from previous diseases of hypercalcemia. The calcium precipitates lodge in the nephron causing elevations of BUN and Creatinine levels.
 
Affected dogs must be treated for malignant hypercalcemia with saline diuresis and monitored closely during and post surgery. Once the primary tumor is excised, the calcium level returns to normal. Recurrence or metastases may be detected upon re-check lab work that shows hypercalcemia.
 
 Perianal Tumors in Cats

Cats rarely develop perianal tumors, but when they do they are recurrent and generally fatal under one year.