Mammary cancer in the dog: a study of 120 cases

Abstract

Of the 120 cases of mammary cancer occurring in 117 female dogs (15 spayed), 2 male dogs, and 1 dog of undetermined sex, 107 (nearly 90%) were observed in dogs 8 to 15 years old. Mammary tumors occurred in nearly 14% of 875 female dogs with neoplasms. Nearly 60% of 128 neoplasms were located in the 4th and 5th mammary glands. Of the 128 cancers in these 120 dogs, 85 were classified as duct carcinoma, 38 as lobular carcinoma, 3 as malignant mixed tumor, and 2 as duct and lobular carcinomas. Most duct carcinomas originated in the epithelial cells of ducts at all levels, and a few arose in previously benign duct papillomas. The lobular carcinomas arose in alveoli and developed into progressively larger lobules. A negative factor in the development of mammary cancer is ovariectomy before or shortly after the first estrous cycle in the dog and before the age of 40 in women. In both dog and man, aging is a positive factor in the development of mammary cancer. In women, other positive factors are nulliparity and inheritance; e.g., a high rate of breast cancer in close female relatives of Jewish extraction. An epidemiologic study of breast cancer in man and dog in high-risk countries(e.g., United States) and low-risk countries (e.g., Japan) is indicated.

PIP: 120 cases of canine mammary cancers were analyzed. 102 were surgical cases, 2 surgical and necropsy cases, and 16 necropsy cases. Of these, 117 were female dogs (15 spayed), 2 were male dogs and 1 was of undetermined sex. Tissues were fixed in 10% formalin and stained with hemotoxylin and eosin. Nearly 90% of mammary cancers occurred in dogs 8 to 15 years old. 128 mammary cancers in the 120 dogs consisted of 85 duct carcinomas; 38 lobular carcinomas; 3 malignant mixed tumors;, and 2 combined duct and lobular carcinomas. There was a lack of clear-cut predilection of any breed of dog in the U.S. for mammary cancer. Duct carcinomas originating in the epithelium at all levels of the duct system are more common than lobular carcinomas arising in the epithelial cells of alveoli proliferated in a progressively enlarging or burgeoning lobular pattern. Ovariectomy before or shortly after the first estrous cycle in the dog and before the age of 40 in women protects against the development of mammary cancer. Aging is a contributing factor in the development of mammary cancer, as are nulliparity and inheritance (e.g., high rate of breast cancer in close female relatives or Jewish extraction). Further study of the human and canine population of Japan and the U.S. should be done to determine the incidence and possible etiologic factors for mammary cancer in the human female and in the bitch.