Mammary Tumors in Dogs

A Guide to Breast Cancer and Mammary Tumors in Dogs: Causes, Symptoms, and Treatment

Katelyn Son
By Katelyn Son
Medically reviewed by JoAnna Pendergrass, DVM
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What is a Mammary Tumor in Dogs?

what is a mammary tumor in dogs

A mammary tumor in dogs is a tumor that stems from abnormal growth in the dog’s breast tissue. Mammary tumors are prevalent in intact female dogs and females spayed after their first heat cycle. Mammary tumors in dogs have a high incidence among certain breeds like Poodles and German Shepherds. Obviously, they are pretty rare in male dogs

There are two types of mammary tumors in dogs:

  • Malignant mammary tumors. Malignant tumors of the mammary glands (breast cancer) are the most common type of cancer in intact female dogs. They usually affect the fourth and fifth mammary glands. Adenocarcinomas and carcinomas are particularly frequent. Malignant cells have a rapid growth rate and quickly invade other internal organs (lungs, regional lymph nodes, bones, and blood vessels). 
  • Benign mammary tumors. Benign tumors of the mammary gland in dogs are non-cancerous, meaning they are not aggressive and do not spread to normal cells of other organs and tissues. The most common form of a benign mammary tumor in dogs is adenoma. 

Although not a tumor, mammary gland hyperplasia can affect a female dog’s mammary glands. Mammary gland hyperplasia is an enlargement of the breast tissue linked with hormonal changes. The breast tissue becomes lumpy during a heat cycle, then returns to normal after the heat cycle. 

The clinical signs and symptoms of the different mammary tumors in dogs are similar. However, the prognosis is different and varies from good to poor, depending on the type and stage of breast tumor. 

Are Mammary Tumors in Dogs Painful? 

Yes, mammary tumors in dogs can be painful. However, there are variations. The benign form of mammary tumors may be painless, especially in the early stages, but malignant tumors are almost always painful.  

The pain is not caused by the tumor itself but by its growth and the complications from that growth. For example, as the tumor grows in size, it can become inflamed, sore, or even ulcerated. Also, the mass may put pressure on the legs and cause limping. 

What Causes Mammary Tumors in Dogs? 

What Causes Mammary Tumors in Dogs

The exact cause of mammary tumors in dogs is hard to determine. Like most cancers, these common tumors are triggered by several risk factors. Let’s take a closer look at the crucial factors that increase the risk of mammary tumors: 

  • Sex. Like human breast cancer is more likely to occur in women, canine mammary tumors are more common in females. Females have larger mammary mass and higher levels of mammary tumor-inducing hormones, namely progesterone and estrogen. 
  • Hormones. Progesterone and estrogen are linked with the development of mammary tumors in dogs. These two reproductive hormones are produced by the ovaries, regulate the heat cycle, and play essential roles during pregnancy. 
  • Age. Mammary tumors are more common in older dogs. Breast tumors are generally diagnosed in dogs seven years of age or older. 
  • Breed. Certain breeds have an increased risk of mammary cancer development. These include Toy and Miniature Poodles, German Shepherds, English Setters, Cocker Spaniels, Boxers, Dachshunds, and Yorkshire Terriers. 
  • Bodyweight. Obese dogs are much more likely to develop mammary tumors. This may be related to diet quality and elevated levels of inflammation that have been linked to different types of cancers. 
  • Spay status. Unspayed dogs are more likely to develop breast cancer. Spaying before the first heat cycle decreases the breast cancer risk to 0.5%. After the first heat, the risk goes up to 8% and then to 26% after the second heat.

What are the Signs of Mammary Cancer in Dogs? 

The main sign of a mammary tumor in dogs is a palpable mass or lump on or near the breast tissue. The mass looks different in different dogs – firm or soft, colored or uncolored, movable or stiff. In the advanced stages, the mass can be ulcerated and start to bleed. 

After metastasis, the signs of mammary cancer are less specific and depend on the organ affected. Some of the clinical signs seen in metastasized mammary cancer include:

  • Lack of appetite 
  • Weight loss
  • Lethargy
  • Difficulty breathing (lungs metastasis)
  • Limping (bone metastasis). 

Diagnosing Mammary Cancer in Dogs 

Diagnosing Mammary Cancer in Dogs 

The general rule is that every diagnostic process starts with a thorough history and physical examination. During the exam, the veterinarian will evaluate the dog’s overall health and determine the tumor’s location, size, and other physical features. The vet will also order blood tests (complete blood count and biochemistry profile), a urinalysis, and imaging tests, including abdominal ultrasound and x-rays.

The suspicion of canine mammary gland tumors can be based on the physical exam. However, the only way to make a definitive diagnosis is to perform a fine-needle aspiration (FNA) or biopsy.  

Fine needle aspiration is a procedure in which the vet extracts a sample of the tumor cells using a fine needle. A biopsy involves the extraction of a tissue sample from the tumor. In both cases, the samples are analyzed under a microscope to determine their cancerous features and grade the tumor.  The tumor grade will classify the tumor according to how the cancer cells look. The more abnormal the cells, the higher the tumor grade.

The vet may then refer the dog to a veterinary oncologist. The aim of the referral is to either achieve a more precise diagnosis or seek specialized treatment. 

How Do You Remove Mammary Tumors in Dogs? 

The primary treatment for canine mammary tumors is surgery. Surgical removal is most effective for small benign tumors that have not metastasized. 

Surgical Removal. The surgical removal of breast tissue is called a mastectomy. There are two types – simple and radical. Simple mastectomy refers to the reduction of the mammary mass and affected gland. In a radical mastectomy, the vet removes the entire mammary chain (gland, connective tissue), as well as the mammary mass. In case of lymph node involvement, the lymph nodes are removed as well. For unspayed female dogs, the vet may also recommend spaying. 

Tumor Shrinking. There is an option for pet owners wondering how to shrink a dog’s tumor. A revolutionary injection Stelfonta by Virbac, is available for dogs with non-metastasized mast cell tumors. Although this tumor-shrinking method is novel, it is efficient and promising for successful canine cancer treatment. 

What Are Other Treatments For Mammary Cancer in Dogs?

What Are Other Treatments For Mammary Cancer in Dogs

If surgery isn’t an option, your vet may recommend chemotherapy or radiation therapy. Sometimes, cancer in dogs treatment is a combination of different approaches. The best treatment plan depends on the type of tumor, tumor size, and the dog’s overall health. 

Chemotherapy. During chemo, a dog is injected with drugs formulated to fight cancer cells. A qualified vet administers chemo, and the frequency and dose differ with each dog. Chemotherapy is advisable for advanced breast cancer that has metastasized. The most commonly used chemo drugs for mammary tumors in dogs are carboplatin and doxorubicin. 

Radiation Therapy. Radiation is an option for treating mammary tumors in dogs. Radiation therapy is recommended for treating incompletely excised but non-metastasized tumors. The downside is that dogs need daily treatment for three to four weeks. 

Hormonal Therapy. In some cases, the vet may recommend hormonal therapy. This can be done before the surgery to decrease the size of the breast mass or after the surgery to prevent future complications.  

Non-Steroid Anti-Inflammatory Drugs. Non-steroid anti-inflammatory drugs (NSAIDs) are prescribed to dogs with inflammatory mammary carcinoma. These drugs reduce inflammation, thus providing relief for the dog. 

Complimentary holistic treatment options can be helpful to improve your dog’s quality of life at home during cancer treatment. Such treatments include acupuncture, physical exercise, and CBD for dogs. Talk with your vet about which complementary would best suit your dog.

Cannabidiol (CBD) Products. The use of cannabidiol (CBD) for cancer patients in veterinary medicine is new but shows promising effects. We suggest CBD products from the high-quality and vet-approved Honest Paws CBD Collection. They are made of organic hemp and are vegan, gluten-free, and human-grade. 

What can I do to Prevent Mammary Cancer in Dogs?

It’s hard to pinpoint exact ways you can protect your dog from mammary cancer. However, there are some ways to minimize the risk of the development of mammary tumors. Here is how to prevent cancer in dogs:

  • Early spaying. Removing a female dog’s ovaries and uterus can lower her chance of getting breast cancer to less than 1%. For spaying to be truly effective, it should be done before the first heat cycle. 
  • Diet. Because obesity is one of the risk factors for developing canine mammary tumors, a healthy diet that supports a healthy weight has a protective effect against breast cancer. In fact, healthy nutrition is important for overall health and may help reduce the risk of breast cancer in dogs. 
  • Regular health checks. Having your dog regularly examined by a qualified vet can help you detect diseases in the early stages when treatment is possible and more effective. Dogs whose cancer is caught in the early stages have the best prognosis, while dogs whose cancer is not diagnosed until late have a poorer prognosis.

Another way you can protect your dog from the potential effects of living with cancer is to secure high-quality treatment by subscribing to a pet health insurance plan. The OneVet insurance plan can make a significant difference in your dog’s veterinary care. It offers unlimited access to a licensed veterinarian and $3,000 in emergency funds. 

Are Mammary Tumors in Dogs Fatal? 

Are Mammary Tumors in Dogs Fatal

Most mammary gland tumors aren’t fatal with early detection and adequate treatment. However, if the disease is allowed to progress into later stages without proper treatment, it can be fatal. 

As a common type of tumor, breast cancer in dogs requires proper attention. To avoid poor outcomes, early detection through regular veterinary checkups is vital.