An adenoma is a benign growth of glandular tissue cells. An adenocarcinoma is a malignant growth of these cells most often originating (primary site) from the intestines, uterus and mammary glands. They often metastasize (spread) to the lungs. Nearly 80% of all lung tumors are adenocarcinomas. Adenocarcinoma is one of the most common types of cancer found in dogs and is the most common primary cancer of the kidney, colon and rectum. If the primary site is the intestinal tract, metastasis to the liver, other abdominal organs and lungs is common. Another primary site for adenocarcinoma is the perianal area. It is the most common perianal tumor in the males. The primary site of perianal adenocarcinoma differs with gender. In females, the anal sac is most often the site of origin, whereas, in males, this is rare. Male perianal adenocarcinomas most commonly arise from the sebaceous glands. These two types of perianal adenocarcinomas differ in another way. The female with anal sac adenocarcinoma has a much worse prognosis because this type is much more invasive. It has been thought, but never proven, that these perianal tumors are hormone-dependent. Older, intact males are more likely to develop perianal adenomas (benign tumors) which resolve with castration. This has not been proven for adenocarcinomas.

CLINICAL SIGNS:

These are dependent on the location of the tumor. If in a kidney, one can see blood in the urine (hematuria), increased frequency of urination (pollakiuria), increased thirst (polydipsia), loss of appetite, weight loss, and abdominal distention. Since adenocarcinomas of the kidney frequently metastasize to the lung, coughing and labored breathing might also be seen. This kidney cancer can also spread to the lymph nodes, liver, spleen, brain and bones where other signs might be noted. Perianal adenocarcinomas are most often seen on the hairless area of the anus, but can extend into haired regions. They can also be seen on the prepuce, scrotum or tailhead . These ulcerated lesions are firmly fixed to underlying tissues. Tumors that progress farther up the intestinal tract can become large enough to cause difficulty expelling stool. Perianal adenocarcinomas often metastasize to lymph nodes and bones of the lower spine. Vertebral fractures and resultant pain would then be seen. Females with anal sac adenocarcinomas often have high serum calcium levels (hypercalcemia) which in itself can cause kidney failure. In addition to the usual signs of kidney failure, hypercalcemia causes muscle weakness that may be misinterpreted as signs of hip dysplasia, spinal arthritis, etc. Adenocarcinomas of the mammary glands are usually felt as non-mobile growths. If local invasion has been aggressive, ulcerative lesions on the skin may be noted.

DIAGNOSIS:

The type of diagnostic test will be dependent on the location of the original tumor. Common diagnostic tests for adenocarcinoma are: physical exam including palpation of lymph nodes and digital rectal exam; blood tests including a complete blood count and serum chemistry panel which includes calcium and albumin, chest x-ray, abdominal x-ray and/or ultrasound, fine-needle aspirate and/or biopsy.

TREATMENT:

Surgery to remove as much tumor as possible as well as removal of affected lymph nodes. Radiation therapy and chemotherapy. Treatment to lower calcium levels if high and to promote kidney function if kidneys are affected.

PROGNOSIS:

Dependent on size of lesion when first diagnosed as well as existence of metastases. The smaller the mass, the better the prognosis. Male dogs with perianal adenocarcinoma may survive for years as long as recurrences are treated as early as possible. This is not true for females with anal sac adenocarcinoma. A recurrence of this tumor or its corresponding high calcium blood level is indicative of the poor prognosis of this very aggressive cancer.

MODE OF INHERITANCE:

Not considered an inherited disease.

REFERENCES:

Foster, R. & Smith, M. What’s the diagnosis?: understanding your dog’s health problems. New York: Howell Book House, 1995; 97, 236-237.

Kirk. Kirk’s current veterinary therapy XII: small animal practice. Philadelphia: W. B. Saunders Co., 1995; p. 466.

Kitchell, B. & Ehrhart, N. Topics in Small Animal Practice. Paper presentation in Rockford, IL, January 1997; 1993

Madewell, Bruce. Cancer. In: Siegal, M, ed. UC Davis school of veterinary medicine book of dogs: a complete medical reference for dogs and puppies. Davis: University of California, 1995; 409.

Ogilvie, G. Selected topics: veterinary oncology. Fort Collins: Colorado State University. Paper presentation in Rockford, IL; January 1997.

The Veterinary Clinics of North America: Small Animal Practice, Vol. 15/#3. Philadelphia: W. B., May 1985. Saunders Co.