Mammary Cancer in Dogs: Vet-Verified Signs, Risks & Treatment

Mammary cancer does not only affect humans. Unfortunately, this disease of the century also occurs very often in pets. In dogs, approximately 80% of all cancer cases affecting the female genital system are mammary (breast) cancers. The risk of this type of cancer increases with the dog's age and each estrous cycle if the dog is not spayed.

Breast cancer in dogs is much more prevalent than you think

Breast cancer represents approximately 40% of all cancer cases in dogs. Clinical signs of mammary cancer in dogs may include weight loss, mammary nodules, matted fur, poor appetite, lethargy, and muscle weakness.

Malignant mammary tumors are indicated by wayward bumps and lumps

Take your dog to the vet if you palpate or notice nodules, growths, lumps, or bumps on or around their mammary glands. These nodules must be tested by a veterinarian to determine if they are cancerous and what type of cancer it is. However, there are situations when the nodules are so small that they cannot be palpated.

A quick note on malignant tumors and their benign counterparts

The key difference between benign and malignant tumors is that benign tumors don't usually progress into cancer. Malignant mammary tumors, however, are the ones that develop into breast cancer in dogs.

In this article, you'll learn seven (7) key things about mammary cancer in dogs: what it is, its risk factors, clinical signs, diagnosis and treatment options, what happens when a tumor ruptures, life expectancy, and more.

#1. What is Mammary Or Breast Cancer In Dogs?

Breast or mammary cancer is the aberrant and out-of-control growth of normal breast tissue cells that undergo mutations. These turn into malignant mammary tumors that grow and spread quickly, feed on the body's resources, and no longer fulfill the functions they had when they were healthy.

Cells in canine mammary tumors divide rapidly, forming a small but fast-growing mass. Initially, the tumor is so small it can't be seen with the naked eye and may even be missed during a general examination by palpation.

Breast cancer in dogs disrupts how the mammary glands work

Malignant tumors affecting the mammary gland can cover a lot of ground in a short span of time. As the tumor cells divide, the tumor begins to grow.

It can grow so much that some dogs simply end up dragging the tumor onto the ground. In other cases, canine mammary tumors grow until they ulcerate, rupture, and bleed. Moreover, the formation of the tumor alters the function of the mammary gland.

If the tumor is malignant, it can spread through the blood and lymphatic systems (or via the lymph nodes), releasing tumor cells that settle in nearby organs. These cells form a new malignant mammary tumor as they go along, disrupting the function of the affected organs—a process called metastasis.

In dogs with malignant mammary tumors, metastasis often occurs in the lungs but can also spread to the kidneys, liver, and regional lymph nodes. The presence of multiple tumors significantly increases the risk for the affected dog.

#2. What Causes Breast Cancer in Dogs?

As mentioned earlier, mammary gland tumors are the most common type of cancer in female dogs. Although rare, males can also develop these tumors. Just to emphasize, breast cancer is one of the main causes of death in canines.

Canine mammary carcinoma is similar in many aspects to breast cancer in humans, sharing pathological, biological, and molecular characteristics. A prominent example is lymph node involvement in developing multiple mammary tumors over time.

Mammary tumors are not only dependent on ovarian hormones (estrogen and progesterone) but also on growth factors, which trigger specific processes in the dog's body. While solitary mammary tumors are common, affected dogs may also develop multiple malignant mixed tumors.

Risk factors to keep in mind

Female dogs have 4 to 5 pairs of mammary glands. These are arranged into two mammary chains or rows, with each chain having 4 to 5 mammary glands. Larger breeds can have less mammary glands, while smaller breeds can have more. Male dogs also have rudimentary nipples and mammary glands.

The mammary glands in all animals are closely related to the reproductive system. The main reason that leads to the occurrence of mammary tumors in dogs is represented by the influence of reproductive hormones.

Therefore, dogs with the highest risk of developing mammary cancers are intact, unspayed female dogs.

This happens because these dogs still have the female reproductive system, which produces hormones. Approximately 50-70% of tumors in female dogs are mammary cancer. The mean age of developing mammary cancer is 7-11 years in all dog breeds. However, mammary cancer is rarely diagnosed in dogs younger than five years old.

An increased risk of developing mammary tumors is also represented by:

• Dogs that eat a diet based on red meat
• Obese dogs
• Purebred dogs
• Small or toy breeds
• Hormonal drugs for interrupting the heat cycle

According to studies, some small-medium breeds are also most prone to developing mammary cancer, such as:

• Dachshunds
• English springer spaniels
• Cocker spaniels
• Boxers

The mean age for these breeds is 7.8 years old. Also, numerous clinical studies have proven that the administration of hormonal drugs to females in heat favors the occurrence of breast cancer.

A low incidence of mammary tumors is found in males but also in female dogs that have had their reproductive system surgically removed (ovariohysterectomy) before their first heat cycle. A significant lower risk in developing mammary tumors is also seen in older intact females that have breast cancer but are also spayed when the tumor is removed.

In general, studies show that spayed females have a risk of developing breast cancer of only 12% compared to intact females. The same study also shows that females spayed before their first heat cycle have only a 0.5% risk of developing breast cancer. As females get into heat and are spayed, the risk of developing breast cancer increases, such as:

• Females that were spayed after their first heat cycle have an approximately 8% risk of developing breast cancer.
• Females that were spayed after two or more heat cycles present a 26% risk.
• Females that were spayed after two or more heat cycles but were sterilized until the age of two and a half years presented a lower risk of developing mammary cancer compared to females past two and a half years.

The conclusion of this study is that females that were spayed after their third heat cycle did not have a lower risk of developing breast cancer.

Studies also show that females that undergo a regional mastectomy when the tumor is removed, present an increased risk of developing new breast tumors in the same mammary chain. (Regional mastectomy means that only the mammary gland affected by cancer is removed.)

As a result, an initial radical mastectomy (that is, the removal of the entire mammary chain when removing the breast tumor) would lead to a lower risk of developing new breast tumors.

#3. Are Mammary Tumors in Dogs Always Cancerous?

You may be wondering if all breast tumors are cancerous. The answer is no. Not all breast tumors are cancerous. In fact, mammary tumors in dogs are 50% benign and 50% malignant.

Comparing benign and malignant tumors

Depending on the speed with which it grows, the degree of dissemination (spreading to the surrounding organs), and the prognosis, a tumor can be:

• Malignant - it spreads to the surrounding organs (i.e., has an invasive character) and can metastasize causing the appearance of other tumors and is not well defined.
• Benign - it is not invasive, it is well-defined, and it does not spread to other organs.

A cancerous tumor can be distinguished from a benign (non-cancerous) one only by histopathological examination.

Mammary tumors vs. mastitis in dogs

If breast tumor means the aberrant multiplication of cancer cells, mastitis means inflammation of the mammary gland. Mastitis in dogs usually occurs during lactation.

Clinical signs of mastitis may include:

• Swelling of the mammary gland
• Redness of the area
• The area is warm to the touch
• The dog shows sensitivity to pain
• Functional limitation
• The mother dog refuses to nurse her puppies and/or lay down
• Panting

Is mastitis in dogs an emergency? Mastitis can be fatal if you do not take your pet to the vet in time. Therefore, it can be considered an emergency.

The diagnosis is most often made by the veterinarian following the general examination. Sometimes additional tests can also be recommended to determine what type of pathogen is causing the infection.

Will mastitis in dogs go away on its own? Mastitis in dogs usually doesn't go away on its own. Therefore, it is advisable to seek professional help. Depending on the causative agent and severity, mastitis can be treated with the following:

• Antibiotic treatment
• Surgical treatment
• Cold compresses
• Milking the gland(s) until the infection has cleared

Can mastitis in dogs burst? If acute mastitis is not treated in time or properly, it can spread to the other mammary glands and can lead to rupture. In addition, the development of abscesses or the appearance of gangrene can lead to sepsis.

Mammary tumors vs. lipomas in dogs

A lipoma is a benign tumor that originates from fatty cells, unlike breast tumors that originate from mammary epithelium cells. Lipomas are also called fatty tumors. They are well-defined nodules of variable sizes around the mammary gland, under the skin. They can also occur anywhere else on or in the dog’s body. Lipomas are also mobile, while most mammary tumors are not.

What is the average age of a dog with lipoma? The chances of lipoma in dogs increase significantly as the pet ages. In general, lipoma occurs in dogs aged between nine and 12 years.

What can be mistaken for a lipoma in dogs?

Fibrosarcomas can be mistaken for lipomas. They have similar consistency—both are rubbery, round, and soft. This type of cancer usually has an unfavorable prognosis because it is an aggressive cancer that spreads at a distance (especially to the regional lymph nodes and lungs).

Moreover, fibrosarcoma has a high tendency to recur. This type of cancer is rare and occurs in elderly females (the mean age is 11.8 years old).

To differentiate lipoma from fibrosarcoma, in addition to the usual procedures administered (i.e. abdominal ultrasound, etc.) the vet must excise the tumor and send it to histopathology for diagnosis.

Can dog lipomas turn into cancer?

Lipomas are benign tumors that, in most cases, do not become cancerous. However, there are rare cases when they can turn into liposarcomas (malignant cancer). Dogs diagnosed with this type of cancer have a good prognosis if the tumor is surgically removed before it spreads to other organs.

#4. Classification of Mammary Tumors in Dogs

As we mentioned before, breast tumors can be malignant or benign. With regard to malignant breast tumors, they are of several types, such as:

• Adenocarcinoma
• Carcinosarcoma
• Solid carcinoma
• Papillary carcinoma
• Complex carcinoma
• Fibrosarcoma

Benign mammary tumors can be:

• Ductal papilloma
• Fibroadenomas
• Simple adenomas
• Benign mixed tumors

#5. Clinical Signs of Breast Tumors in Dogs

Breast tumors can vary in consistency, size, and shape. They can be attached to the underlying tissue or mobile; they can have a soft, rubbery, or hard consistency. Some dogs can develop several tumors in different mammary glands (in 50-70% of cases), while others develop one tumor in a single mammary gland.

The skin can also be ulcerated in some cases of mammary carcinomas.

Lymph nodes that are regional in nature (axillary and superficial inguinal) can be increased in volume. This depends on the duration of tumor growth, its type, and its size.

Dogs with metastases can also present the following clinical signs:

• Fatigue
• Lack of appetite
• Weakening
• Apathy
• Panting
• Matt fur
• Nausea

Can a dog’s mammary tumor rupture or burst?

Why is my dog’s mammary tumor bleeding? In advanced cases, in which the breast tumor grows significantly, it can ulcerate (open up and start bleeding). In severe cases, the breast tumor can rupture, leading to great pain and discomfort.

How long can a dog live with a ruptured mammary tumor? Ruptured mammary tumors in dogs can become infected and lead to sepsis, which can be fatal. Therefore, for these reasons, it is advisable to take your dog to the vet from the first clinical signs and not wait for the tumor to overgrow and burst/rupture.

#6. How Long Will a Dog Live with a Mammary Tumor?

Mainly, the survival time depends on the type of tumor and whether it has metastasized or not. It also depends on the administered treatment. In malignant mammary cancer, the survival time is usually less than a year.

Some studies show that dogs with inflammatory mammary cancer that were treated with palliative therapy and chemotherapy lived longer than those that were treated with palliative therapy alone. Inflammatory mammary carcinoma and sarcoma have a poor prognosis—dogs diagnosed with these types of cancer live weeks or months, the most.

For benign mammary cancer, dogs have an excellent prognosis.

#7. How Is Mammary Cancer in Dogs Treated?

Mainly, breast tumors are treated by surgical excision. As mentioned previously, to reduce the risk of recurrence, it is recommended to remove the entire mammary chain and spay the female (if it is intact) when the tumor is removed.

In some cases, a complete regional mastectomy isn't possible due to the tumor's size or location. When the tumor infiltrates the abdominal muscle, full surgical removal becomes nearly impossible. In these situations, treatments to shrink the tumor and improve surgical options are recommended.

The vet can also recommend additional treatment after surgical resection and biopsy (which helps determine the type of cancer). Cancers with a low risk of metastasis do not require systemic treatment (chemotherapy). For cancers with a high risk of metastasis or for inoperable tumors, chemotherapy is recommended. Some examples of chemotherapy drugs are: doxorubicin, cisplatin, carboplatin, cyclophosphamide, and vincristine.

Other treatments can be:

• Electrochemotherapy
• Radiotherapy
• Hormonal therapy

How do you treat mammary tumor bleeding in dogs? If your dog’s mammary tumor starts to bleed, it is better to go with your pet to the vet. Usually, the first-line treatment in bleeding mammary tumors is surgical removal. However, if there is just a minor bleeding, clean the area with warm water and apply a protective bandage to cover the area. If the bleeding does not stop, take your pet to the vet as soon as possible.

How do you treat mammary tumor ulceration in dogs? Mammary tumor ulceration is only treated at the vet. Dogs with ulcerated tumors have a grave prognosis than those with non-ulcerated mammary tumors. For this reason, it is necessary to go to the veterinary clinic as soon as possible.

Alternative Treatment—Can Mammary Cancer in Dogs Be Treated Naturally?

If your dog has been diagnosed with breast cancer and you're concerned about the potential side effects of chemotherapy, there are natural options available that can support your dog's fight against cancer. One of these options is PIPTOPET, a product containing Fomitopsis betulina, a medicinal mushroom used for centuries due to its wide range of health benefits. This mushroom is known for its antioxidant, anti-inflammatory, antibacterial, antiviral, and antitumor properties, which are supported by scientific research.

In cases of mammary tumors, combining surgical removal with homeopathic treatments like PIPTOPET can help improve your dog's quality of life and potentially extend their life expectancy.

In addition to PIPTOPET, you might also consider AGARICUS mushroom supplement, which is known for their immune-boosting and antitumor properties. Agaricus mushrooms can help enhance your pet’s natural defenses.

Agaricus mushroom (Agaricus blazei) is a medicinal mushroom with many benefits, particularly for pets dealing with cancer, including mammary cancer. Here are some key benefits of Agaricus mushrooms in supporting pets with mammary cancer:

• Boosts Immune System: Agaricus mushrooms are rich in beta-glucans, which help stimulate the immune system. A stronger immune system enables the body to fight cancer cells more effectively, offering better overall support in battling mammary cancer.
• Antitumor Properties: Scientific studies have shown that Agaricus mushrooms contain compounds that help inhibit the growth of tumors. This makes it beneficial in slowing down the progression of mammary cancer.
• Anti-Inflammatory Properties: Inflammation is a common issue in cancer, and Agaricus mushrooms possess strong anti-inflammatory properties.
• Enhances Quality of Life: By supporting immune function, reducing inflammation, and fighting oxidative stress, Agaricus mushrooms can improve the overall quality of life for dogs with mammary cancer. Pets may experience better energy levels and less discomfort during this time.

If you are thinking of trying chemotherapy for your dog, remember that CBD oil, in combination with chemotherapeutics such as vinblastine and mitoxantrone, can have better results than chemotherapy alone.

About the author

Denise Lessard

HOMEOPATH, NATUROPATH, REFLEXOLOGIST, TRADITIONAL CHINESE MEDICINE THERAPIST

Denyse Lessard is deemed as the “mother” of Zumalka, which was established more than ten years ago to provide easily accessible natural products for pet wellness worldwide.

Besides being a trained alternative medicine therapist, Denyse also has expertise in homeopathy, naturopathy and iridology, reflexology, as well as Chinese medicine. She is a long-standing member of the Professional Union of Homeopaths of Quebec, as well as the Association of Naturopaths and Naturotherapists of Quebec.

Denyse’s philosophy as regards pet wellness is not just about only dealing with disease and illness when they get in the picture, but keeping animals in ideal health each and every day.

Find out more about Denyse when you click HERE.