Mammary cancer, or breast cancer, in cats is quite serious. The majority (over 90%) of mammary tumors in cats are malignant or cancerous. They tend to be extremely aggressive cancers and spread very rapidly. This is in sharp contrast to mammary cancer in dogs, where 50% or less of mammary tumors are malignant.
Why Do Cats Get Mammary Cancer?
We don't entirely know why one cat may develop a malignant form of breast cancer and the next may not. However, there are several things we do know.
- Unspayed female cats are more likely to develop mammary cancer than spayed female cats. This is especially true if the cat is spayed at a young age. If spayed after two years of age, there is no change in the incidence of mammary cancer compared to unspayed cats. (However, there still are other health benefits for cats that are spayed after two years of age.)
- Mammary cancers are more common in older cats than in younger.
- Whether or not a cat has had kittens does not seem to affect her chance of developing mammary cancer.
- The Siamese breed appears to be more likely to develop breast cancer than other breeds of cats. They also seem more likely to show symptoms at a younger age.
- Exposure to certain hormones (progestins) can make a cat more likely to develop mammary cancer. This is not as problematic currently as it was in the past. Progestin products were used to correct some types of behavioral issues in the past but their use for this purpose is no longer common.
What Happens When a Cat Gets Mammary Cancer?
The tumor may start out as a small nodule palpable within the breast tissue of any of the mammary glands. With time, this nodule is likely to increase in size and growth can happen very quickly with malignant forms of cancer.
Besides the initial tumor, mammary tumors in cats can spread to other mammary glands and cause similar lesions in those glands. They can also spread to the local lymph nodes and to other parts of the body. Metastasis (spread) to the lungs is fairly common with these cancers. If the lungs become affected, the cat may experience difficulty breathing or may begin to cough.
As the tumors increase in size, they frequently will break through the skin and will bleed and ooze fluid. These lesions may become quite uncomfortable for the cat, particularly for those cats that are meticulous groomers.
Types of Feline Mammary (Breast) Cancer
Carcinomas and adenocarcinomas are the most commonly seen types of mammary tumors in cats. Both of these tumor types are considered to be malignant.
Mammary tumors are graded depending on the cellular structure of the tumor. Grade 1 tumors are more likely to have a longer survival time (over one year). Grade 3 tumors are the most aggressive and cats diagnosed with grade 3 mammary tumors generally do not survive for long after diagnosis (less than one year for most.)
Is There Treatment for Feline Mammary Cancer?
Surgical removal of the tumor while it is still small is the optimum form of treatment. Removing the tumor before it reaches a large size increases the odds that the entire tumor may be surgically removed before it begins to spread. Surgical removal of a feline mammary tumor should be radical, with a wide surgical excision unless the tumor has already reached an advanced stage where complete removal is not likely. In many cases, the entire chain of mammary glands is removed.
In the advanced stages of mammary cancer, partial removal of the tumor may be attempted to provide relief from the necrotic (dead) tissue and discharge that occurs when a tumor breaks through the skin. This is a palliative measure aimed at securing some degree of comfort for the cat, not at curing the cancer.
Chemotherapy is usually recommended following surgical removal. Chemotherapy agents used may include adriamycin, cyclophosphamide and carboplastin. However, newer medications that may be effective in treating some forms of cancer are starting to become available as well and oncologists continue to search for the most effective medications.
Preventing Breast Cancer (Mammary Cancer) in Cats
Mammary cancer should be a concern for anyone who owns a female cat. Spaying the cat prior to 6 months of age drastically reduces the probability of breast cancer later in life. If spaying is delayed, the probability increases and after two years of age, the protective benefits of spaying in regards to the development of mammary cancer are eliminated completely. Therefore, it is recommended to spay your cat prior to six months of age.
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