Mammary Gland Tumors in Dogs

Mammary Gland Tumors in Dogs

By: Dr. Jeffrey Philibert

Section: Information In-depth

Swelling of the breast tissue can be related to a number of conditions – both normal and abnormal. For example, normal hormonal changes associated with the female reproductive cycle in nonspayed females lead to enlargement of the mammary glands. Pregnancy is of course related to glandular development. Inflammation, hyperplasia (excessive growth), and cancers are examples of abnormal growth. When mammary glands are enlarged or swollen, a veterinarian will consider a number of diagnoses.

  • Mammary gland tumor (neoplasia). Approximately 50 percent of mammary gland tumors are benign. The other 50 percent are malignant, and of these, about 50 percent will metastasize elsewhere in the body.

  • Mastitis is an infection of the mammary glands that causes swelling of the glands and mimics cancer. The glands are usually warm to the touch, painful, and can discharge discolored milk.
    Mastitis is most often observed in association with the female estrus cycle (heat), during pseudocyesis (false pregnancy) or after a dog has given birth. Animals with mastitis frequently are very ill with fever or other signs of infection. In contrast, most dogs with breast cancer are not ill unless the cancer spreads.

  • Cysts, papillary cystic hyperplasia, and lobular hyperplasia are benign conditions affecting the mammary glands in which proliferation or growth of normal tissue structures is accompanied by fluid production forming cysts (pockets of fluid).

  • Inflammatory carcinoma is a more aggressive form of mammary gland tumor seen primarily in the dog in which all glands in one or both chains are affected. Severe bruising, and ulceration of the overlying skin are accompanied by an animal that feels very sick. This particular form of mammary gland cancer is very likely to spread throughout the body and it carries a very poor prognosis.

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