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Mammary Tumours

While mammary tumours are the most common cancer in unspayed female dogs or those that were desexed after their first or second heats, they are rare in cats and male dogs.

Unfortunately, over 85% of the mammary tumours that do occur in cats are aggressively malignant and the prognosis is always poor.


Mammary tumours are usually first detected as small, nobbly lumps underneath the skin, located in and around the mammary glands. Sometimes the tumour will ulcerate and become painful and inflamed. The rate of growth and spread varies with the type of tumour.


The most effective treatment is early surgical removal combined with desexing if the cat is entire. By early we mean removing the lumps when they are still small. Given the propensity for mammary tumours in cats is to be malignant, early intervention is critical. 

Surgical resection in cats must be aggressive with removal of one or preferably both sets of mammary glands recommended. The prognosis is always guarded.

CVH vets may recommend taking x-rays of the chest to check for signs of spread before surgery and taking a biopsy to determine if the tumours are benign or malignant.

The role and benefits of chemotherapy and radiation in cats and dogs with malignant mammary tumors is not yet clear, but consultation with a veterinary cancer specialist may be recommended.


In female cats, it is well documented that desexing early (before the first or second heat) reduces the risk of mammary tumours significantly.

The American College of Veterinary Surgeons state that cats spayed before 6 months of age have a 7 times reduced risk of developing mammary cancer and spaying at any age reduces the risk of mammary tumors by 40% to 60% in cats.

Examine your pet at regular intervals for any lumps, bumps, or swellings and make sure you get any lumps checked quickly while small.