Mammary gland tumors are a type of cancer that arises from breast tissues. About 50 percent of these tumors are malignant, which means they can spread, and 50 percent are benign and do not spread.

The cause of mammary tumors is not well understood. Hormones such as estrogen and progesterone play an elusive role in the development and progression of these tumors. They occur in both intact and spayed dogs and it is the most common cancer of female dogs. Mammary gland tumors occur most commonly in females; they are rare in males.

The average age that pets develop these tumors is 10 to 12 years of age. Dog breeds that appear to be at increased risk are poodles, terrier breeds, cocker spaniels, and German shepherd dogs.  Spaying pets early in life will significantly decrease the risk of developing mammary gland tumors later in life.

Diagnosis and Treatment Notes:

  • Mammary gland tumor is generally diagnosed by biopsy or fine needle aspirate of the mass and chest x-rays. Bloodwork, abdominal x-rays and abdominal ultrasound may be recommended.
  • Treatment depends on the severity of the disease, your individual pet, and your veterinarian. The surgical removal of the mass and associated mammary tissue (mastectomy) is recommended. Un-spayed pets should be spayed. In pets with a malignant tumor, chemotherapy, radiation therapy and/or anti-estrogen therapy may be recommended. Discuss treatment details when your pet is diagnosed with this condition.


What to Watch for*:

  • Masses or lumps within the mammary glands
  • Bruising of the skin over the mammary glands
  • Ulceration (open wounds) on the mammary glands
  • Bleeding of the skin associated with growth of the masses
  • Difficulty breathing
  • Coughing
  • Lack of ability to exercise
  • Lack of appetite

*Please notify us if you notice any of the above signs or if you have any questions!