Cat Breast Cancer: What You Need to Know

Dr. Margaret McEntee, a professor of Veterinary Oncology at Cornell University's College of Veterinary Medicine, explains, ‘a cat has two “chains” of four mammary glands and nipples running parallel on each side of its belly.’ It is along this mammary chain that breast cancer is found in the cat. The tumour often starts so small it is easily missed by even the most attentive pet parents. The mass is most often located just beneath or next to one of the nipples, though anywhere along the breast chain or the surrounding tissue is possible.

To move forward with a diagnosis, your vet may recommend two diagnostic tests: 

Radiographs (X-rays):

Radiographs will help your vet see if there is already obvious spread of a tumour to your cat’s lungs or other organs.

Biopsies:

Biopsies are samples of the affected tissue. These are then examined at a microscopic level to see if the cells are cancerous and if they are malignant or benign.

These tests allow your vet to avoid confusing mammary tumors with non-dangerous overgrowth of mammary tissue, called mammary hypertrophy. While nursing, cats may also develop swollen breast tissue for other reasons, including mastitis, an infection of the breast tissue, or a clogged milk duct. If you see any abnormal swelling, it’s best to contact your veterinarian as soon as possible.

Before any kind of treatment is undertaken, your vet will want to stage the tumour and check for other health problems. Staging will tell your vet how serious the tumour is and whether it has spread. Blood and urine tests for concurrent health problems are important. Most cats with mammary (breast) cancer are older cats so may have other issues like kidney disease.

There are four stages of breast cancer in cats, which are outlined below, however the treatment of each varies somewhat by stage.

Stage 1:

Tumour is less than 2 cm, no spread to lymph nodes or other organs.

Stage 2:

Tumour is 2-3 cm, no spread to lymph nodes or other organs.

Stage 3:

Tumour is less than 3 cm and there is spread to lymph nodes, but not other organs, OR tumour is more than 3 cm and may involve lymph nodes but not other organs.

Stage 4:

Tumour is any size, may involve lymph nodes and has spread to other organs.

If your cat is diagnosed with breast cancer that your vet feels can and should be treated, the most common treatment is surgery to remove the mammary tissue. Depending on the type of tumour and how aggressive it is, your vet may opt to remove all the mammary tissue, not just the area with the lump(s).

In some cases, surgery will be sufficient, but if there is any sign of spread, your vet may also want to use chemotherapy as well as surgery to ensure the best prognosis for your cat. Cats generally experience fewer and less severe side effects from chemotherapy than humans because a gentler dose and less intense schedule is typically used in cats. While cats may sometimes experience an upset stomach from chemotherapy, they usually do not experience hair loss like people do.

The prognosis varies depending on the stage of the tumour. Some cats will live for more than three years after surgery, while others may only have four to six months. This is why it’s important to have as much information as possible prior to embarking on treatment and discuss the situation fully with your vet.

You can never guarantee that your cat won’t get breast cancer, but you can make a massive difference in their cancer risk by spaying them. It’s thought that spaying before the first season reduces the risk by over 90%! In a world where there are far too many unwanted cats, spaying makes absolute sense for so many reasons. These days, many vets are happy to neuter cats at around 4 months of age. Talk to your vet about the best timing for your individual cat.

Obesity is also a risk factor for cancer in general, so keeping your cat slim and active throughout life is a good idea and can prevent many health problems.

‘Cancer’ is a scary word, and one that none of us wants to hear for us or our pets, but it’s sadly a fact of life for many.  If, for some reason, you are not going to spay your cat, be vigilant. From a young age, get them used to being gently handled and stroked all over. This way, you can regularly check their mammary tissue for anything out of the ordinary. The more you know what is normal for your cat, the earlier you will spot anomalies.

Regular vet visits are essential for health in general. Throughout life, a yearly examination is essential. As your cat ages, your vet will probably suggest that this becomes more frequent. Every 6 months is often recommended for senior cats. 

We all want as long as possible with our beloved animals, so being vigilant at home and keeping a good veterinary schedule are great ways to make sure that happens. Hopefully, breast cancer will never be something you and your cat have to tackle, but being prepared and knowing what to look for will put you ahead of the game if it does happen.

What are the early signs of breast cancer in cats?

 The most common signs are lumps in the mammary (breast) tissue. You may see ulcerated or bleeding patches as well. 

Can breast cancer in cats be treated?

In many cases, yes, if it’s detected early enough. The smaller the tumour, the better the prognosis. Surgery is often utilized to remove the mammary tissue. Some may need chemotherapy as well.

How can I prevent breast cancer in my cat? 

By far the best way to prevent breast cancer in cats is spaying. Spaying before the first season or heat reduces the risk of breast cancer by over 90%.

What increases the risk of breast cancer in cats? 

The main risk factors are:

1. Not being spayed (by far the most important factor).

2. Age. Older cats are more at risk.

3. Breed. Some breeds such as Siamese seem to be more prone.

4. Sex. It’s rare, but male cats can get breast cancer too. Females are at much greater risk.

Reviewed by Becky Mullis, DVM, DACVIM (Nutrition) and Emma Milne BVSc FRCVS.