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Mammary Cancer in Dogs

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Mammary Cancer in Dogs

Posted by Sara Ochoa on
Updated at: February 18, 2021

Mammary Cancer in Dogs | Innovet Pet

Cancer is a disease that knows no bounds, meaning it has the ability to develop in just about any part of the body. For dogs, there are a plethora of cancers that they are at risk of encountering at some point in their lives.

Of course, the number one hope is that our dogs never have to deal with a cancer diagnosis or experience the taxing impact of cancer treatments. But as wonderful it would be to live in a world where cancer didn't exist, we have yet to find a definitive cure for the aggressive disease, so a cancer-free world is not a reality yet.

It’s possible that someday, your dog might show symptoms of cancer. The best thing to do when faced with the possibility of cancer is to be as educated and prepared as possible, especially when it comes to mammary tumors.

When the cells of your dog’s mammary glands start to grow rapidly, some of the cells might experience a slight change, which then creates an abundance of abnormal cells. When these abnormal cells grow and multiply, over and over again, mammary gland tumors in dogs come to life.

Can Dogs Get Breast Cancer?

Just like people, dogs can get breast cancer. “Breast” is simply another name for “mammary.” There are many other names for cancer of the mammary glands in dogs, but we will dive into that discussion in a moment.

First, it’s important to identify which dogs can get breast cancer and which dogs cannot. Did you know that it’s not only possible for female canines to have mammary gland cancer, but male dogs as well? Sometimes, people get confused as to how it’s possible for male dogs, as well as all male species, to contract this form of cancer when the development of male mammary glands is vastly different from breast development in female dogs.

The confusion stems from not understanding that even though there are distinct differences between male and female breasts, males still have breast tissue. So, just like females, male dogs can both be diagnosed with mammary cancer because mammary glands are part of the male anatomy. The difference in breast development has more to do with the ability to lactate for females, and the lack thereof in males.

But breast cancer has nothing to do with whether or not a dog can lactate. Instead, it has everything to do with whether or not a dog has breast tissue, seeing as that is where the cancerous cells originate.

Which Breeds Does It Affect?

Certain breeds of dog are more likely to develop mammary tumors. These breeds include...

  • Boxers
  • Brittany Spaniels
  • Chihuahuas
  • Cocker Spaniels
  • Dachshunds
  • Dobermans
  • English Setters
  • Poodles
  • Yorkshire Terriers

These breeds are at a higher risk of developing mammary gland tumors in dogs, but that shouldn’t stop you from adopting these breeds and giving them a loving home. With all other risk factors, just because you have dogs that belong to one of these nine breeds doesn’t mean your dogs will automatically develop this form of cancer at some point in their lives. These breeds are simply at a higher risk for developing mammary tumors based on analytics and statistics of dogs with malignant mammary tumors.

The Many Different Names of Canine Mammary Cancer

Did you know there are many different ways to describe cancerous mammary gland tumors in dogs? Other names include… 

  • Breast Cancer
  • Mammary Adenocarcinoma
  • Mammary Carcinoma

Canine Mammary Cancer in Female Dogs

Canine mammary tumors are not rare in dogs. They are not recognized as one of the most common types of canine mixed tumors, and this is primarily due to the fact that they only affect one of two canine genders, so the statistics are already lower than other types of cancer in dogs.

Even so, around fifty percent of all canine mammary tumors are categorized as malignant, meaning the cancer does not just stay locally in the region of the mammary glands. Instead, malignant tumors start in the mammary glands and move throughout the body by invading regional lymph nodes.

When cancer cells start to travel within your dog's body by way of regional lymph nodes, the phenomenon is known as metastasizing. The regional lymph nodes carry the cancerous cells through the lymph system, offering cancerous cells the opportunity to invade other parts of the body, too. All it takes is one lymph node.

CBD OIL FOR DOGS | Innovet Pet Products

It's an incredibly dangerous scenario for a dog to be in because not only is it more difficult to treat cancer that spreads to other parts of the body but it is also a very fast-acting process as well. Among the female dogs that become ill with malignant tumors, the majority of the dogs have not been spayed.

Many dog owners have their female dogs spayed as young puppies in an effort to prevent their female dogs from becoming pregnant later on down the road. It's a very responsible move for dog owners to make if they know that they do not want to have an entire litter of dogs in the future. But pet owners don't always opt for the spaying process for the sake of avoiding canine reproduction.

Instead, many pet owners will have their female dogs spayed as a preventative measure. By spaying your female puppies, you reduce the risk of developing mammary tumors for your dog and the likelihood that they will become sick, especially if your female dogs are spayed before their second heat cycle. Getting your dog spayed before their very first heat cycle is preferred and encouraged, but this isn't always possible.

As long as dogs are spayed prior to their second heat cycle, the likelihood that they will be diagnosed with the condition in their later years is much lower. Most female dogs don't show symptoms until they are around ten years old, and dogs are more likely to be diagnosed around the age of eleven, so this disease zeroes in on older dogs.

On top of spaying your female dogs before their first two heat cycles, another way you can lower the risk of developing the disease is to keep them at a healthy weight. Obesity in dogs is a risk factor, as is the overconsumption of fatty foods. Make sure your dog's dietary intake is well rounded, and you'll increase the chances of your dog never coming face-to-face with a breast cancer diagnosis.


Symptoms of Breast Cancer in Dogs | Innovet Pet

The most obvious sign is a lump on the breast. The mass will be tangible, and it won't be external, but rather like a growth that is situated underneath your dog's skin. For dogs, the lump will be near the abdominal region. Taking your hand, and making sure your dog is comfortable, gently feel around their abdomen, paying close attention to anything that feels bumpy and out of place.

Canine mammary tumors are not one-size-fits-all, so the mass could be of literally any tumor size and shape, though most pet owners report that their dogs had a very firm lump in a somewhat rounded shape. A mammary tumor usually juts out a bit, too, so it's not completely flat. In rare cases, it is possible for the mass under the skin also known as a nodule to pop open, causing blood to flow out of the cancerous mammary tumors. 

In even more uncommon cases, the exposed mammary tumors will also emit an abnormal discharge, which is another clear sign. This doesn’t always happen, nor does it absolutely have to happen in order for a dog to have canine breast cancer.

A few other symptoms of canine mammary tumors are…

  • Moving more slowly than usual
  • Difficulty breathing like normal
  • A whistling sound whenever your dog inhales
  • Weight loss paired with little to no appetite
  • Soreness around the abdomen
  • Standing up over laying down
  • Relaxing on their sides rather than their stomachs
  • Whimpering or crying
How Cancer is Diagnosed in Dogs | Innovet Pet

How It’s Diagnosed

In order to properly diagnose dogs, veterinarians will go through an overall analysis of the dog's medical history, as well as discuss the dog's behavior and demeanor with the pet owner. There are a few different scenarios that the vet looks for and seeks to rule out before looking into the mammaries more closely.

If your dog has been through a heat cycle recently, then it might be a contributing factor to the cancer-like symptoms. Also, giving birth to puppies can result in after effects that mirror mammary cancer symptoms in many ways, so your dog's vet will inquire about a recent pregnancy, too. Additionally, your dog might have experienced a false pregnancy, or pseudopregnancy, which would elicit similar symptoms as well.

Once these three possibilities, as well as many others, have been accounted for and ruled out, your dog's vet will take a closer look at your dog's tumor-like mass. It's normal for the vet to perform a few physical tests as well, like a blood count exam, or one of many urine tests.

The goal is to evaluate the overall functioning of your dog's body to narrow down the possible causes that are at play, especially if a surgical removal is necessary. Veterinarians need to ensure that the dog is healthy enough to undergo cancer treatments as well, should that be the next necessary step.

A few other examples of ways that the disease is diagnosed include...

  • Abdominal ultrasounds
  • CT scans
  • Fine-needle biopsies
  • Lymph node exam 
  • X-rays of the chest


As similar as each case can appear to be on the surface, the truth of the matter is that all canine mixed tumors in dogs are unique. As a result, the treatment plan for a dog with malignant mammary tissue will be dependent upon the small details. Even so, the majority of dogs with malignant mammary tumors in dogs undergo surgery to remove the abnormal mammary tissue.

  • Biopsies of mammary gland
  • Chemotherapy treatments
  • Radiation therapy
  • NSAIDs for pain
  • Surgical removal
  • Tumor removal
HEMP DOG TREATS | Innovet Pet Products

The risk of developing mammary tumors is out of our control because it’s either genetic or by chance. But even though the risk of developing mammary tumors is hard to predict, treating mammary tumors is possible. From inflammatory mammary tumors, to benign tumors and malignant mammary tumors, early detection leads to early treatment.

Malignant mammary tumors in dogs should be treated as soon as they are spotted, especially because of the aggressive nature that malignant mammary tumors have. Some can be benign, but other mammary tumors can be malignant, but no matter what, mammary tumors in dogs are not invincible. Discuss your dog’s treatment options with a veterinarian you trust with your dog’s health.

How Long Can a Dog Live with Mammary Tumors? 

It's difficult to say an exact estimate regarding the survival time of dogs with this condition. The reason the survival times of dogs depends on the situation is that a plethora of factors go into the overall prognosis.

For example, the size of a mammary tumor can vary drastically from one dog to the next. A larger tumor is going to be more difficult to shrink, remove, and treat than a tumor of a much smaller size. Also, there are different types of mammary tumors in dogs, despite the fact that the dogs have the same kind of cancer.

Other factors that impact the prognosis include...

  • The type of invasion that is present
  • Whether or not the cancer has metastasized
  • The role regional lymph nodes play in the situation
  • The way the body is locally responding to the cancer cells

Since there isn’t a definitive answer as to how long a dog can live with the condition, the best plan of action is to pay attention to any warning signs that you might see. If you notice your dog expressing any of the symptoms, seek out medical advice immediately. The earlier your dog is treated for canine mammary cancer, the more likely it is that the cancer will become benign tumors. In the best case scenario, your dog will make a full recovery.


Mammary gland
Malignant Mammary Tumors in Dogs
Mammary Tumors in Dogs
Mammary Tumors


Approved by:
Dr. Sara Ochoa
Doctor of Veterinary Medicine, St. Georges University

Sara Redding Ochoa, DVM was raised in north Louisiana. She graduated from LA Tech in 2011 with a degree in animal science. She then moved to Grenada West Indies for veterinary school. She completed her clinical year at Louisiana State University and graduated in 2015 from St. George’s University. Since veterinary school she has been working at a small animal and exotic veterinary clinic in east Texas, where she has experience treating all species that walk in the hospital. In her free time, she likes to travel with her husband Greg, bake yummy desserts and spend time with her 4-legged fur kids, a dog Ruby, a cat Oliver James “OJ”, a rabbit BamBam and a tortoise MonkeyMan.

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The Innovet Team

Please do not ask for emergency or specific medical questions about your pets in the comments. Innovet Pet Products is unable to provide you with specific medical advice or counseling. A detailed physical exam, patient history, and an established veterinarian are required to provide specific medical advice. If you are worried that your pet requires emergency attention or if you have specific medical questions related to your pet’s current or chronic health conditions, please contact or visit your local/preferred veterinarian, an animal-specific poison control hotline, or your local emergency veterinary care center.

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