MAMMARY CANCER IN CATS
We have all heard of breast cancer in women. With approximately one woman in eight or nine falling victim to this form of cancer, there are awareness campaigns from numerous health care agencies and research is on-going. Every woman is encouraged to check for breast lumps regularly. But what about pets? It turns out our furry friends (mostly female but male as well) are also at risk for this very common form of cancer. The mammary cancer picture is a little different between cats and dogs. The information on this page concerns the situation for our feline friends. In the cat, mammary cancer is the third most common cancer, with the most common victim being a senior female cat around age 10-12 years who either remains unspayed or was spayed well into adulthood.
Tumors spread from the mammary glands to local lymph nodes and then on to the chest, brain, bone, and even spleen. Expect chest radiographs to assess tumor spread to the lung to be needed before surgery can proceed. Basic blood tests will also be needed.
Early spay is the single most significant protective factor. Spaying before age 6 months results in a 91% reduction in risk. Spaying before age 1 year results in an 86% reduction in risk. Spaying before age 2 years leads to an 11% reduction in risk. Having given birth to kittens has no effect on mammary cancer risk for cats. Spaying after age 2 years does not reduce the risk of mammary cancer development at all.
TYPES OF TUMORS
Feline mammary tumors are generally either carcinomas or adenocarcinomas. Papillary or tubular carcinomas tend to be the least aggressive. Ductular carcinomas seem to kill cats about four times faster. Anaplastic carcinomas are the worst kind, usually dispatching the patient three times faster than that.
The pathologist examining the biopsy tissue uses different cellular criteria of malignancy to grade the tumor as Grade I, Grade II, or Grade III. A grade I tumor generally has a good chance of a one year survival time depending on its size and tumor type. Grade II tumors have a 57% chance at survival after a year unless chemotherapy accompanies surgery. Grade III tumors treated with surgery alone had no survivors at one year from the time of diagnosis.
If only one side is involved, and the tumor is deemed to be in an early enough state for cure to be possible, one should consider prophylactic removal of the unaffected mammary chain (i.e. the other side) as the factors that led to tumor development on the first side undoubtedly still apply to the (as yet) unaffected side. A period of 3-5 weeks is generally allowed between surgeries to ensure stretching of the skin so that there is room to close the second incision.
If only one side is involved but is deemed too advanced for cure, it is likely not worth removal of the second mammary chain.
Aggressive surgery yields a disease free interval of 1 year in about 50% of cats and 2 years in 32% of cats.
If lymph node involvement is already present at the time of surgery or if the tumor recurs after the first surgery,
If the tumor is in an obviously advanced state at the time of the first surgery, then a less aggressive surgery to palliate the infection may be more appropriate. This will at least make the cat more comfortable by losing the smelly, infected external tumor. Alternatively, radiation therapy can be used "dry up" the stinky leaking gland temporarily, especially if the cancer poses too great an anesthetic risk for tumor removal.
For the most up to date information on chemotherapy, we recommend an appointment with a veterinary oncologist.
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There are two problems which tend to lead to the demise of the cat. One is simply the infected ulcerated external tumor. The primary tumor smells rotten and bleeds. Secondary tumors arise and also break through the skin. Cats are fastidious creatures and do not like having growths of this type on their bodies plus owners tend not to like rotten, bleeding flesh in their homes. Cats are commonly euthanized due to the progress of the external tumor.
The other problem is tumor spread to the chest. The lungs are invaded by tumor cells and ultimately the cat will not be able to breathe.
Cats with advanced lung involvement at the time the tumor is diagnosed have a median survival time of only one month.
Life quality decisions for cancer patients are difficult as the disease progresses inexorably but slowly and there are good days mixed with bad days. Quality of life issues center around inherent discomfort from the disease versus enjoyment of other aspects of life (socialization, appetite etc.). Criteria for a euthanasia decision are largely personal but some guidelines have been established to assist in making this difficult decision. Please visit our Euthanasia page to view the "Quality of Life" scale to assist you in determining when the time is right. Remember, your veterinarian is available to discuss life quality issues if you need additional guidance.
Information in this article was largely drawn from Wypij, J., Fan, T.M., de Lorimer L. Malignant mammary tumors: Biological behavior, prognostic factors, and therapeutic approach in cats. Veterinary Medicine June 2006, p352-366. as well as Dr. Philip J. Bergman's presentation on Feline Mammary Tumors at the 2013 ABVP meeting.
Page last updated: 7/21/2016