Summary

A perianal adenocarcinoma is an uncommon tumor that arises from the sebaceous glands surrounding the anus. Intact males, recently castrated males, and males castrated late in their lives are most at risk. In intact males, these tumors may also be associated with testicular tumors.

These masses are considered malignant. As such, they tend to spread to distant sites and may be locally invasive. The local lymph nodes and lungs are the sites most commonly affected by perianal adenocarcinoma metastasis.

The benign version of this disease is called perianal adenoma and it’s considered far more common than the perianal adencarcinoma. In most cases, perianal adenoma carries a very good prognosis (after treatment, they recur in less than 10% of patients).

By contrast, perianal adenocarcinoma is considered an aggressive tumor type and carries a fair prognosis. Though local recurrence is common after treatment, 70% live more than two years after being diagnosed, if treated.

Symptoms and Identification

Perianal adenocarcinomas appear as non-painful masses around the anus. They usually emerge in the hairless area of the perineum, but technically, they can appear in the prepuce, scrotum, and under the tail.

They typically arise as single masses that are often ulcerated and infected on their surface. They tend to be locally invasive as well, adhering to underlying tissues as they expand and grow.

Additional signs of a perianal carcinoma may be related to its sensitive location: straining to defecate, local irritation, and perirectal pain are common. Constipation and even obstipation can occur with larger masses that prevent normal bowel movements.

Diagnosis of perianal adenocarcinomas is typically achieved by biopsying the tissue, as simple cell analysis (cytology) is usually unable to differentiate between a benign and malignant tumor type.

A rectal examination, X-ray and/or ultrasound may help determine whether the local lymph nodes are affected. An ultrasound-guided biopsy of these is recommended. Chest X-rays can help reveal whether the lungs are involved. .

Affected Breeds

While all breeds of dogs may suffer from perianal adenocarcinomas, the German Shepherd and Arctic Circle breeds of dog are known to be predisposed.

Treatment

The treatment for a perianal adenocarcinoma typically involves wide resection of the mass, whenever possible. Unfortunately, most masses are so invasive that they aren’t completely amenable to surgical treatment. Moreover, recurrence of these masses is common and re-growth is typically even less resectable than the tumor’s initial appearance.

In incompletely resectable or non-resectable cases, chemotherapy and/or radiation are recommended for best results (i.e., most comfort and longevity). When affected, removing the local lymph nodes is also highly recommended.

In these cases, it’s important to note that castration is considered of minuscule benefit.

Veterinary Cost

The cost of treating perianal adenocarcinomas depends on the size, invasiveness and presence of metastases (distant spread) of the tumor as well as the level of care elected and the geographic region.

Initial diagnosis (biopsy and X-rays) typically costs about $500 to $1,000. Surgical resection may cost upwards of two or three thousand dollars. For pets that require additional treatments, including radiation therapy and chemotherapy, treatment $5,000 to $10,000 is not considered unusual.

Prevention

These tumors are largely preventable by castrating male dogs early on in their lives. However, care should be taken to consult with a veterinarian during a dog’s adolescence by way of assessing all the risks and benefits of sterilization –– for both males and females.



References

Berrocal A. Vos, J.H. van den Ingh, T.S.G.A.M. Molenbeek, R.F. vanSluijs, F.J. Journal of Veterinary Medicine Series A. Volume 36, Issue 1-10, pages 739–749, February-December 1989

Vail, D. M.; Withrow, S. J.; Schwarz, P. D.; Powers, B. E. Perianal adenocarcinoma in the canine male: a retrospective study of 41 cases. Journal of the American Animal Hospital Association 1990 Vol. 26 No. 3 pp. 329-334

Wilson GP, Hayes HM Jr. Journal of the American Veterinary Medical Association [1979, 174(12):1301-1303]

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