Mammary Tumors
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Mammary Tumors in Dogs and Cats: What Do I Tell the Owner?
I consider mammary neoplasia to be one of the great embarrassments of veterinary pathology, for we have historically been excessively pessimistic about the behavior of these tumors in both dogs and cats. Most of the attention has been paid to mammary tumors in dogs. Based on a review of the worldwide literature, 50% of canine mammary tumors are described as histologically malignant. That piece of information has, unfortunately, been translated into predictions of 50% behavioral malignancy. This is a massive overestimate of the true malignancy of canine mammary tumors. The mistake is in assuming that the histologic criteria of malignancy can be applied equally to all kinds of tumors. What we have discovered, in the last 10 years or so, is that these criteria of malignancy need to be interpreted differently for each kind of tumor, so that things like hyperchromasia and high mitotic index may signal the kiss of death when found in one kind of tumor, yet be quite irrelevant to prognosis for another.
In order to assist you in giving the appropriate prognostic information to owners concerned about mammary neoplasia in their pets, I have listed for you some of the more recent information about the behavior of mammary tumors in both dogs and cats.
Dogs:
Cats:
Mammary tumors in cats have not been as thoroughly studied as they have in dogs, probably because the overall prevalence is substantially lower. In contrast to the estimate of a 50% prevalence of macroscopic tumors in intact bitches, the prevalence in cats is estimated at approximately 25 tumors per 100,000 cats. Their relative infrequency is counterbalanced, however, by a much greater malignancy.
Brian Wilcock, D.V.M., PhD.
wilcock@histovet.com
21 Vardon Drive, Guelph, Ont. N1G 1W8
Toll Free Phone/Fax: 1-800-853-PATH
Outside Canada: 519-822-4486

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