Mammary Gland Tumor in Dogs

Benign and malignant tumors of the mammary glands occur fairly frequently in unspayed female dogs, in fact they are the most common type of tumor in the group. Spaying can largely reduce the risk of developing this type of cancer, especially if the dog is spayed before it has an opportunity to go into heat. There are two main types of mammary gland breast tumors, each with several subtypes of tumor growth.

The mammary glands’ function is to produce milk to feed newborn puppies. They are located in two rows that extend from the chest to the lower abdominal area; the nipples indicate their location on the trunk of the body. While this condition is more likely to occur in the female population, it does also affect male dogs, albeit rarely. When a male dog is affected by a tumor of the breast, the prognosis is much more guarded and grave.

A genetic basis is possible in some breeds, and there are frequently some genes that can be identified in dogs that are predisposed to cancer of the mammary glands. For example, toy and miniature poodles, English springer spaniels, Brittanys, cocker spaniels, English setters, pointers, German shepherd dogs, Maltese, and Yorkshire terriers have been reported to have an increased risk of developing breast or mammary tumors compared to other breeds. Median age is about 10.5 years (range, 1 to 15 years of age); it is less common in dogs younger than five.

Symptoms and Types

  • Usually slow-growing single or multiple masses in the mammary glands – about half of patients have multiple tumors
  • May have superficial loss of tissue on the surface of the skin over the mammary tissue, frequently with inflammation
  • Mass may be freely movable, which implies benign behavior
  • May be fixed to skin or body wall, which implies malignant behavior or cancer

About half of affected dogs will be diagnosed with the benign form of mammary tumors, which may be classified as complex adenomas, simple adenomas, fibroadenomas, and duct papillomas. The approximate other half of dogs to be diagnosed with mammary tumors will have a malignant form of tumor, which may be osteosarcomas, fibrosarcomas, solid carcinomas, and papillary cystic adenocarcinomas, amongst others.


Unknown, although likely hormonal or genetic.


Several diseases could account for the symptoms, so your veterinarian will want to rule them out before arriving at a conclusion. You will need to give a thorough history of your dog’s health and onset of symptoms.

A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, and a urinalysis. Diagnostics will include X-rays of the chest and abdomen, which may detect metastasis. It will be necessary to conduct a biopsy of the mass to fully determine its nature, whether benign or malignant. In addition, the lymph nodes will be examined, and a sample taken from them for laboratory analysis.


The surgical removal of the breasts or mammary glands in an animal

mammary glands

The glands in female animals that are used to produce milk; also called the udder or breast


The prediction of a disease’s outcome in advance


An in-depth examination of the properties of urine; used to determine the presence or absence of illness


The disappearance of the signs and symptoms of a particular disease; this is often used in association with cancer


Something that becomes worse or life threatening as it spreads


A small lump or mass of tissue

lymph nodes

Small structures that filter out the lymph and store lymphocytes


The process of removing tissue to examine it, usually for medical reasons.


Having two sides


Not being able to cause harm; the opposite of malignant.


A female dog that has not been spayed.

estrous cycle

The reproductive cycle of female animals


Denotes an animal that is still able to reproduce or is free of cuts and scrapes


The time period in which a female is receptive to male attention


The result of a malignant growth of the tissue of the epithelial gland.

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