Breast Cancer in Dogs: Prevention, Causes, Treatments, and Prognosis

Breast-cancer-in-dogs

Breast Cancer in Dogs: Prevention, Causes, Treatments, and Prognosis

Mammary cancer is the most commonly occurring of all cancers in female dogs. Despite its prevalence, discovering lumps along your male or female dog’s abdomen can be alarming. 

Thankfully, around half of all mammary tumors are benign and can easily be treated surgically. Malignant tumors, on the other hand, are not so straightforward. 

This article discusses the most common types of mammary tumors, their symptoms, methods of diagnosis, treatment options, and prognosis.

Key Takeaways 

  • Female dogs are more likely to develop breast cancer than male dogs.
  • Older dogs, especially those over six years of age, are at a higher risk of mammary tumors.
  • Tumors can develop in one mammary gland or more.
  • Female dogs spayed before their first heat have a 0.5% chance of developing mammary cancer. Females spayed before their second heat have an 8% chance.
  • Symptoms of breast cancer in dogs include weight loss, lumps along the abdomen, and swollen teats.
  • X-rays, blood tests, biopsies, and a physical examination can confirm the presence of mammary cancer.
  • Treatment options include surgery, radiation therapy, and chemotherapy.

What Are the Symptoms of Mammary Cancer in Dogs?

Knowing the signs of cancer in dogs and detecting it early on is essential to provide the best chance of treatment and recovery. 

The symptoms of mammary tumors in dogs include: 

  • Weight-loss [1]
  • Loss of appetite
  • Exercise aversion
  • Difficulty urinating
  • Labored breathing
  • Painful, swollen breasts
  • Discharge from mammary glands
  • Weakness [2]
  • Growing lumps along the abdomen
  • Discharge from the nipples

What Does Breast Cancer Look Like In a Female Dog?

The primary sign of breast cancer in dogs is a lump, or lumps, in the mammary glands. Most dogs have between eight and ten nipples and typically develop about five mammary glands, with each teat having 7-16 duct openings [3]. Mammary tumors usually start as tiny lumps but grow rapidly.

The tumors can be felt in or near the nipple, and the size and appearance of the lumps vary according to the type of tumor. Some may appear red, swollen, and inflamed, while other lumps could be hard or soft. 

Breast Cancer in Dogs Pictures

(for the graphic designer, create a graphic with photos of the different manifestations of breast cancer in dogs)

tumor

cancer

What Are the Causes of Breast Cancer in Dogs?

Mammary tumors are the most common cancer developed in female dogs [4]. Despite its prevalence, the causes of breast cancer in dogs are not thoroughly understood. However, there is some evidence that exposure to increased progesterone levels could cause cancer development [5]. 

Progesterone stimulates the secretion of growth hormone—tumors develop due to cancer cells dividing and growing uncontrollably [6][7]. The increased levels of growth hormone could cause these rapidly multiplying cells to do so even faster, leading to the development of mammary cancer.

What Factors Increase the Risk of Developing Breast Cancer?

Although there is no way to predict whether or not your pet may develop mammary cancer, some factors could increase its chances:

  • Gender: Female dogs are 62 times more likely to develop mammary cancer than male dogs [8][9]. Male dogs with mammary cancer also typically only develop benign tumors, which provide a better prognosis than malignant ones.
  • Spayed status: The age at which a dog is spayed or neutered could also play a role in the risk of cancer development. If a dog is spayed before her first heat cycle, the chance of developing mammary tumors is 0.5%. If spayed before her second heat cycle, the probability is 8% [10]
  • Breed: Some breeds of dogs are more prone to developing tumors. The complete list of breeds can be found below.
  • Age: Dogs over six years of age are more likely to have mammary cancer than younger ones [11]
  • Diet: Feeding your dog a diet of home-made food consisting of lots of beef and pork, as well as obesity early on in your dog’s life, could increase its chances of developing mammary tumors [12]
What Factors Increase the Risk of Developing Breast Cancer
Spaying your dog after her second heat cycle increases the chance of breast cancer to 26%

What Breeds of Dogs Get Breast Cancer?

Just as female dogs are more prone to developing breast cancer, certain breeds also have a higher risk [13, 14]: 

  • Afghan Hounds
  • Beagles
  • Bichon Frise
  • Boxers
  • Chihuahuas
  • Cocker Spaniels
  • Dachshunds
  • Dobermanns
  • Poodles, including miniature and toy breeds
  • English Spaniels
  • English Setters
  • German Shepherds
  • Pointers
  • Samoyeds
  • Schnauzers
  • Terriers, especially Yorkshire Terriers

Types of Mammary Tumors

The diagnostic process of possible mammary cancer can identify the type of tumor your pet has. Some of the most well-known include: 

    • Inflammatory carcinoma: This is the most malignant type and could rapidly spread throughout the dog’s body.
    • Adenocarcinoma: One of the most common types of tumors [15
    • Fibroadenoma: A type of benign tumor that is typically painless [16]
    • Mixed mammary tumor: The most frequently occurring tumor in dogs [17]

Dog Breast Cancer: Diagnosis

Early detection of mammary masses is vital to your dog’s correct diagnosis and treatment.

Before the diagnostic process begins, your veterinarian will ascertain whether your dog has recently given birth or gone through a heat cycle. 

Mammary gland hyperplasia produces lumps around the time of a female dog’s heat cycle. Hyperplasia is caused by hormonal imbalance [18]. It typically dissipates once the hormones return to their usual concentration.

Physical Examination

A physical examination can confirm the presence of a tumor in your dog’s mammary glands. The examination can be done at a veterinary clinic and involves a vet examining the teats and any lumps present beneath or around the nipples.

However, a physical examination of your pet cannot determine the type of tumor present. To do this, further tests are required. 

Imaging Tests

Once the mammary gland that has the tumor is identified, further imaging tests like chest x-rays, a CT scan, or abdominal ultrasound may be conducted to gauge the extent of the mammary tumor growth [19].

Bloodwork and Urinalysis

A urinalysis and complete blood count can help assess whether the tumor has affected any other organs or bodily functions. These tests are also helpful in deciding if your dog is the right candidate for surgical removal of the tumor.

Fine Needle Aspiration

A fine-needle aspiration (FN) is a type of biopsy during which a veterinarian inserts a needle into the tumor and withdraws a tissue or fluid sample. Fine needle aspiration can help your vet determine whether the mammary mass is a cyst or cancer.

If a large enough sample is taken, an FNA could help identify whether or not the tumor is malignant [20].

Biopsy

Your veterinarian will conduct a biopsy to identify the type of tumor your pet has. The vet will remove a small part of the tumor, which can be studied under a microscope to determine precisely what kind of growth your dog has.

Breast Cancer Treatment in Dogs

Once a vet has concluded their diagnosis, the type of tumor present will help them recommend the best treatment options.

Surgery

Surgical tumor removal is still the most commonly recommended method for treating breast cancer in dogs [21]. 

During the procedure, which can be done in a veterinary hospital, as much mammary tissue as is reasonable is removed to ensure the gland containing the tumor is eliminated. 

If more than one tumor is present, surgical removal of the entire mammary chain may be necessary. 

Dog Breast Cancer Surgery Cost 

The cost of mammary tumor removal depends on the number and size of the growths present. 

Surgery to remove one mammary gland typically costs about $500. For removal of a mammary chain, a total mastectomy may cost more than $1,000 – $2,000.

Spaying Intact Dogs

Besides spaying your dog before her first heat cycle, which helps to reduce the risk of developing mammary tumors, it could also help increase the life expectancy of dogs with mammary tumors if done less than two years before tumor surgery [22].

Spaying Intact Dogs
Spaying a dog with mammary tumors less than two years before surgery can increase life expectancy significantly

Chemotherapy

Chemotherapy alone for the treatment of malignant mammary tumors has not yet been proven effective. However, chemotherapy after the surgical removal of malignant tumors can help increase your pet’s survival time [23].

Radiotherapy

Early radiation therapy for dogs with confirmed malignant mammary tumors can help prevent cancer spread (metastasis). Radiation therapy is especially beneficial to dogs with inflammatory mammary carcinoma and can significantly increase average survival times [24].

Clinical Trials for Dogs with Breast Cancer

Treatments for mammary tumors in dogs are constantly evolving. Some of the most promising clinical trials are discussed below.

Oncolytic Virotherapy

The administration of a recombinant measles virus has shown promise in slowing down the progression of tumor growth [25]. 

Flutamide Administration

Flutamide is an anti-androgen, or anti-testosterone, drug. Despite most tests of the drug’s effectiveness being conducted on mice, the administration of flutamide has been shown to inhibit metastasis and reduce tumor sizes [26].

Adjuvant Oxytocin or Desmopressin

In aggressive cases of mammary tumors, surgery may not be enough to increase survival time. Treatment with oxytocin or desmopressin may have beneficial effects on simple carcinomas, although further studies are required [27].

Dog Breast Cancer Prognosis: What to Expect

One of the most significant factors that affect your pet’s prognosis and life expectancy is early detection. 

  • Benign or malignant: A dog with a benign tumor has a far better prognosis than a malignant tumor. Benign tumors grow at a much slower rate and therefore are easier to treat.
  • Size of the tumor: The earlier a tumor is detected, the smaller it will be in size, and the better your dog’s chances of survival.
  • Metastasis: The spread of malignant tumors can result in a significantly poorer prognosis. The spread of a carcinoma or malignant tumor to the lymph nodes usually indicates an unfortunately low survival rate [28]. The lymph nodes connect to several major body organs, which could decrease your pet’s survival time should the cancer reach them.
  • Ulceration: Ulceration is a sign of a highly malignant tumor, possibly inflammatory carcinoma [29]. It’s usually a sign of a poor prognosis.
  • Age: The older the dog, the greater the possibility of developing multiple tumors, decreasing overall life expectancy.

Mammary cancer in dogs progresses in stages and the later your dog is treated, the lower its chance of survival.

Dog Mammary Cancer Stages

There are five stages of mammary tumors in dogs. The stage of your pet’s cancer could help determine the right treatment, prognosis, and life expectancy. 

The characteristics of each stage follow the tumor size (T), spread to regional lymph nodes (N), and distant metastasis (M) [30]. 

Details on each stage are listed below:

Stage 1

  • Tumor size: Less than 3cm
  • Lymph node spread: None
  • Distant metastasis: None

Stage 2

  • Tumor size: 3-5cm
  • Lymph node spread: None
  • Distant metastasis: None

Stage 3

  • Tumor size: Larger than 5cm
  • Lymph node spread: None
  • Distant metastasis: None

Stage 4

  • Tumor size: Any
  • Lymph node spread: Some evidence of regional spread
  • Distant metastasis: None

Stage 5

  • Tumor size: Any
  • Lymph node spread: Regional spread present
  • Distant metastasis: Distant metastasis present

Dog Mammary Tumor Removal Recovery

Dogs with mammary tumors are often treated with surgery, after which your pet may need chemotherapy or palliative care. This can be provided through veterinarian-prescribed medicine and alternative remedies. Most of these treatments are aimed at reducing pain.

Recommended recovery aids include: 

    • Non-steroidal anti-inflammatory drugs (NSAIDs): NSAIDs are commonly prescribed for the treatment of pain and inflammation. They could also reduce the rate at which cancer cells proliferate [31].
    • Ivermectin: Ivermectin has shown promising results as an anti-cancer agent, reducing the growth of tumors in dogs [32]. 
  • Cannabidiol (CBD): CBD has shown promise in reducing cancer cell proliferation [33]. CBD can also significantly reduce the pain experienced in dogs with benign or malignant mammary tumors during and after treatment [34].
Dog Mammary Tumor Removal Recovery
CBD oil showed to reduce pain in dogs with cancer significantly compared to placebo

Breast Cancer in Dogs Life Expectancy

The life expectancy of a dog with mammary tumors depends on several factors, including:

  • The type of cancer: Dogs with inflammatory mammary carcinoma have an average survival time of 25-60 days [35].  Dogs with mild malignant tumors can live for more than two years after treatment [36]. Benign tumors detected early on and treated quickly can leave your pet with a long, healthy life.
  • Spread to lymph nodes: Once cancer spreads to the lymph nodes, life expectancy is drastically reduced despite treatment.

When to Euthanize a Dog with Breast Cancer

Putting a beloved pet to sleep is never easy but must be considered once mammary cancer has spread or progressed too far. 

If your pet shows any of the following signs, you may need to discuss possible euthanization with your veterinarian:

  • Refusal to eat for extended periods
  • Continual vomiting or diarrhea
  • Lethargy
  • Difficulty moving

If you notice any drastic negative change in your dog’s behavior, monitor them carefully and consult your vet to discuss your options.

FAQ

Below are some of the most frequently asked questions regarding breast cancer in dogs.

Is Mammary Cancer in Dogs Painful?

Benign mammary tumors are not typically painful. However, the characteristics of rapid growth and inflammation in malignant mammary tumors can be extremely painful as they progress and enlarge.

Can Breast Cancer in Dogs Be Cured?

Benign tumors make up about half of all breast cancers in dogs. Benign mammary tumors can be treated with surgery and should not significantly affect your pet’s life expectancy. 

About half of the dogs with malignant mammary tumors will experience metastasis, which is extremely difficult to treat.

How Long Do Dogs With Breast Cancer Live?

Average life expectancy after diagnosis and treatment could be anything between 35 days with inflammatory mammary cancer and several years for those with benign tumors.

Survival times for dogs with breast cancer vary greatly depending on the tumor type and growth rate. 

What Are the End Stages of Breast Cancer in Dogs?

The final stages of breast cancer in dogs usually start once the tumor has metastasized to other organs. At this point, there is very little that can be done to treat your pet, and you may need to consider euthanization or palliative care to make your dog’s last days as comfortable as possible.

How Common Are Benign Mammary Tumors in Dogs?

Mammary cancer is relatively common in dogs. At least 17% of dogs with mammary lesions will be diagnosed with mammary tumors, and half of these will be benign [37].

Conclusion

Any type of cancer in dogs can be a scary diagnosis. Due to the prevalence of breast cancer in dogs, it is essential to familiarize yourself with the symptoms, diagnostic tests, and treatment options available should your pet show signs of illness or a behavioral change. 

Thankfully, most mammary tumors can be treated and, if caught early enough, can be successfully treated to provide your dog with a long, healthy life.

References:

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