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

What is mammary gland tumour?

Mammary gland tumours are similar to breast tumours in people, it is the third most common tumour in the cat. 80-90% of mammary gland tumours are malignant, adenocarcinomas being the most common. Carcinoma and sarcoma are less common mammary cancers.

The average age of cats with mammary gland tumours is 10-12 years old. Intact females are at the greatest risk. Spaying, especially prior to their first heat greatly reduces their risk of developing mammary cancer, suggesting that hormonal influence may be involved. However, it can also occur in spayed females and males, but it is rare. 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.

Symptoms of mammary gland tumour in cats:

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. These are numbered 1 to 4. 1 being closest to the head. 1 and 2 are the most commonly involved pairs.

Typical symptoms of mammary gland tumour include:

  • Painless, firm, nodular mass in one or more mammary glands.
  • Ulceration of the skin.
  • Infection, swelling and pain may also be noticed.

Diagnosis and treatment of mammary gland tumour:

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.

Other  tests he may wish to perform include;

  • Radiographs to determine the size of the tumour and to check for signs of metastasis.
  • Fine needle aspirate of local lymph nodes to determine if the tumour has spread.
  • Blood work such as complete blood count and biochemical profile to determine the general health of your cat.


As 80-90% of mammary gland tumours are malignant, surgical excision and histopathology (examination of the removed tissue) are the procedure of choice. This may be a lumpectomy for a small, singular tumour, mastectomy (removal of only the affected gland), radical mastectomy (removal of the entire mammary chain and associated lymph nodes).

Chemotherapy may be recommended for cats if the cancer has metastasized or if it is inoperable.

Prognosis:

  • Cats with a tumour smaller than 2cm have a median survival rate of 3 years.
  • Cats with a tumour between 2-3cm have a median survival rate of 2 years.
  • Cats with a tumour greater than 3cm have a median survival rate of 6 months.

Related content:

Cancer in cats   Cat symptoms