April 27, 2012
Mammary (breast) Tumors in Dogs

What is a mammary tumor?

This is any tumor originating from the mammary gland tissues. In the dog, most tumors of this type are cured by complete surgical removal, but over time a few progress to malignancy and start to spread to other parts of the body (metastasis). A dog may have multiple tumors in different mammary glands.{{more}}

What do we know about the cause?

The reason why a particular pet may develop this, or any cancer, is not straightforward. Cancer is often the culmination of a series of circumstances that come together for the unfortunate individual.

Some animals have a genetic tendency to develop cancer and this risk increases with increasing age. However, sex hormones are the most important single risk factor for mammary tumors in dogs. If the ovaries and uterus are removed (ovariohysterectomy or spaying) at an early age, there is less risk of these tumors developing.

Are these common tumors?

These are very common tumors in female dogs, mainly in middle-aged to older animals. They are rare in male dogs.

The incidence of mammary tumors is between eight and twenty-six percent when dogs are spayed after the first oestrus (heat). Spaying bitches before first oestrus reduces the incidence to 0.5%, so this will affect the probability of your dog developing more mammary tumors.

How will these cancers affect my pet?

The most obvious effect is a lump or multiple lumps in the glands. Some tumors produce a secretion (clear, milky or bloodstained fluid, which may be expressed from the teat). Benign tumors rarely ulcerate or bleed, but large tumors may have physical effects by pressing on the surrounding tissues or structures, or may lose some of their blood supply, causing parts of them to die. Inflammation and secondary bacterial infections are possible, causing pain and general signs of illness.

How are these cancers diagnosed?

Your veterinarian will often suspect the diagnosis of a mammary tumor based on its typical appearance and location. However, accurate diagnosis of the type of mammary tumor relies upon microscopic examination of tissue.

What types of treatment are available?

The most common treatment is surgical removal of the cancerous tissue. Sometimes this is just the lump and sometimes the whole gland and draining lymph node are removed. If there are several tumors, your veterinarian may perform a “radical mastectomy” in which multiple glands and their associated lymph nodes will be removed.

Ovariohysterectomy (spaying) early in life markedly reduces the incidence of mammary cancer. Spaying at the time of tumor removal does not affect growths that are already cancerous, but can make some mammary hyperplasias disappear. Spaying at the time of tumor removal is unlikely to prevent further tumor development.

Are there any risks to my family or other pets?

No, these are not infectious tumors and are not transmitted from pet to pet or from pets to people.

For further information, contact: Dr Collin Boyle
Unique Animal Care Co. Ltd. Tel: 456 4981