Cat Mammary (Breast) Cancer-Symptoms, Diagnosis & Treatment


Mammary cancer in cats


Mammary gland tumours are similar to breast tumours in people, and it is the third most common tumour in the cat. 85-95% of mammary gland tumours are malignant, and adenocarcinomas are the most common type of malignant neoplasm of the breast in cats.

The average age of cats with mammary gland tumours is 10-12 years old. Intact females are at the highest risk. Spaying, especially before their first heat dramatically reduces their risk of mammary cancer, before the mammary glands are exposed to the sex hormones estrogen and progesterone. 

Mammary cancer can also occur in males (approximately 1% of cases are in male cats), but it is rare. Domestic shorthairs and Siamese cats appear to be at an increased risk of developing mammary gland tumours at a younger age.

Fifty percent of cats have tumours in multiple glands. Metastasis (spread of the tumour) is common and will often involve regional lymph nodes, lungs, and the liver.

Mammary cancer in cats facts


Cats have four pairs of mammary glands, the four on the left-hand side are a chain and the four on the right-hand side are a chain. The first two rows of nipples are most commonly affected.

Typical symptoms of mammary gland tumour include:

  • Firm, nodular mass in or around one or more mammary glands
  • Ulceration of the skin which does not heal
  • Unexplained weight loss
  • Milky or bloody discharge from the nipple
  • Infection, swelling, and pain

Can male cats get breast cancer?

Yes, just like human males, male cats can get breast cancer, although it is much less common than in females.


Your veterinarian will perform a complete physical examination, including carefully examining the mass and palpitating the regional lymph nodes to determine if the tumour has spread.

Diagnostic tests: 

  • Fine needle aspirate of the mass as well as local lymph nodes to determine if the mass is made up of breast tissue and determine if the tumour has spread.
  • Radiographs to determine the size of the tumour and to check for signs of metastasis to the chest and/or lymph nodes.
  • Baseline tests which include biochemical profile, complete blood count, and urinalysis to evaluate the overall health of your cat and determine its pre-surgery status.


As 80-90% of mammary gland tumours are malignant, surgical excision and histopathology (examination of the removed tissue) are the procedure of choice.

  • Radical mastectomy (removal of the entire mammary chain), at least on the affected side, but your surgeon may also recommend removing both chains and associated lymph nodes.

Chemotherapy with doxorubicin and cyclophosphamide or carboplatin will be necessary if the cancer has metastasised or is inoperable.


Prognosis depends on the size of the tumour:

  • Smaller than 2cm have a median survival rate of 3 years.
  • Between 2-3cm have a median survival rate of 2 years.
  • Greater than 3cm have a median survival rate of 6 months.


The best way to reduce a cat’s chances of developing mammary glands is to spay or neuter it. One study found that spaying cats before six months reduce the incidence of mammary cancer by 91 percent, and 85 percent for cats spayed before one year of age.

Perform monthly checks on your cat (male and female); this should include evaluation of the mammary glands to feel and feel for changes which include lumps and/or areas of ulceration. See your veterinarian immediately if you notice any chances.