Unfortunately, most people have experienced the devastation of breast cancer, either through a personal diagnosis or the diagnosis of a loved one. As we continue to examine cancer in our pets during Pet Cancer Awareness Month, we should keep in mind that breast cancer can also strike our feline family members.
Mammary tumors are the third most common cancer in cats, and senior female cats between 10 and 12 years of age are most commonly affected. Siamese cats also seem to be overrepresented in this type of cancer.
Though our canine friends develop mammary tumors as well, only about half of those tumors are malignant (meaning that they spread and can be fatal). Unfortunately for our cats, over 90% of mammary tumors are malignant, rapidly spreading to nearby mammary glands and local lymph nodes.
Usually, cats have eight mammary glands, arranged in two rows of four. The most common sites for mammary tumors are the top pair (closest to the forelegs) and the bottom pair (closest to the rear legs) of mammary glands. Owners of older female cats should routinely feel for lumps or bumps on all mammary glands.
The smaller the mass is when it is removed, the longer the median survival time can be. When mammary masses are removed when they are less than two centimeters in size, a patient’s estimated survival time is four and a half years. Considering that most patients are elderly when diagnosed, this may be a normal life span for them. However, if a mammary mass is three centimeters or larger, the median survival time decreases to just six months.
Treatment consists of surgery to remove not only the affected gland, but the entire chain of glands. If both chains of mammary glands are involved, both will need to be removed, although this often cannot be completed in one surgery. To maximize the disease-free interval, pet parents may want to consider adjunctive chemotherapy.
Mammary tumors are fatal for one of two reasons. The first is progression of the external tumor. These tumors grow rapidly and become ulcerated and necrotic. Euthanasia is often pursued due to infected, ulcerated tumors. The other reason mammary tumors are fatal is the cancer’s spread to the chest.
By far, the easiest way to prevent mammary tumors is to have your cat spayed before she is six months old. Doing so will decrease her risk of developing mammary cancer by 91%! Additionally:
- Spaying before one year of age decreases her risk by 86%.
- Spaying before two years of age decreases her risk by 11%.
- Spaying after two years of age does not decrease her risk.
- Having one or more litters of kittens does not decrease her risk.
Whether your kitty is spayed or not, make sure to check her regularly for lumps, and call your veterinarian if you find anything out of the ordinary.