Mammary Tumors in Dogs and Cats

Mammary tumors are frequently observed in older, intact female dogs and cats, originating from the mammary tissue. Detecting a mass during a physical examination in the caudal abdominal and cranial thoracic mammary glands in dogs and cats, respectively, raises suspicion of a mammary tumor. Confirming the diagnosis through histopathology is crucial for determining appropriate treatment and prognosis. While surgical removal of the tumor and regional lymph nodes can extend disease-free time, it may not significantly increase survival time in cases of malignancy.

Prevalence and Variations Across Species

Mammary neoplasia prevalence varies significantly across different species. Dogs are the most commonly affected domestic species, with a prevalence approximately three times higher than in women. In fact, mammary tumors account for around 50% of all tumors in female dogs. On the other hand, mammary tumors are rare in cows, mares, goats, ewes, and sows. Notably, there are notable differences in both the biological behavior and histology of mammary tumors in dogs and cats. Around 45% of canine mammary tumors are malignant, whereas approximately 90% of feline mammary tumors are malignant. Dogs also exhibit a higher occurrence of complex and mixed tumors compared to cats.

Etiology and Risk Factors

The exact cause of mammary tumors remains unknown in most species, except for mice where an oncornavirus is causative in certain inbred strains. Hormones are believed to play a significant role in the hyperplasia and neoplasia of mammary tissue, although the precise mechanism is still unclear. Mammary tumor cells in animals have been found to possess estrogen or progesterone receptors, which may influence the pathogenesis of hormone-induced mammary neoplasia and the response to hormone therapy.

Genetic and nutritional factors have been identified as potential contributors to mammary neoplasia in mice and some humans, but their impact on dogs and cats is not yet well understood. In humans, the BRCA1 and BRCA2 genes are strongly associated with mammary tumors. In dogs, specific genetic variations in the BRCA1 gene have been linked to canine mammary tumors. Additionally, the consumption of red meat, obesity at an early age, and obesity before diagnosis have been linked to an increased risk of mammary gland tumors in intact or spayed dogs.

Clinical Presentation and Behavior

From a practical standpoint, it is important to consider all mammary tumors as potentially malignant, regardless of their size or the number of glands involved. The spread of mammary carcinomas in both dogs and cats primarily occurs to regional lymph nodes and lungs. In dogs, approximately 5%–10% of mammary carcinomas may produce skeletal metastases, primarily in the axial skeleton and long bones.

Canine Mammary Tumors

Dogs have the highest incidence of mammary neoplasia among domestic species, especially in intact female dogs. Approximately 50% of all tumors in female dogs are mammary tumors, with the two posterior mammary glands being more commonly affected. Grossly, the tumors appear as single or multiple nodules, ranging in size from 1 to 25 cm, with a lobulated, gray-tan, and firm cut surface. More than 50% of canine mammary tumors are benign mixed tumors, while a smaller percentage are malignant mixed tumors. The World Health Organization classifies canine mammary gland tumors into various types based on tumor extent, lymph node involvement, and presence of metastatic lesions.

Feline Mammary Tumors

Mammary tumors in cats are most commonly found in older intact females. Spaying cats Significantly reduces the risk of developing mammary tumors, with the incidence being much lower in spayed cats compared to intact ones. Similar to dogs, mammary tumors in cats can present as single or multiple masses, varying in size and consistency. They are often firm, irregularly shaped, and may be attached to the skin or underlying tissues. Feline mammary tumors are more frequently malignant, with the majority being adenocarcinomas. These tumors can be locally invasive and have a higher propensity for metastasis to regional lymph nodes, lungs, and other distant organs.

Recognizing the Symptoms of Mammary Tumors in Dogs

Mammary tumors in dogs can manifest with various symptoms, and it is important for dog owners to be aware of these signs to facilitate early detection and prompt veterinary intervention. While mammary tumors can occur in any mammary gland, they are most commonly found in the caudal abdominal mammary glands.

Here are some common symptoms associated with mammary tumors in dogs:

  1. Presence of a Mass: The most noticeable sign is the presence of a palpable mass or lump in the mammary gland area. These masses may vary in size, ranging from small nodules to larger tumors. It is crucial to regularly perform gentle palpation of your dog’s mammary glands to check for any abnormalities.
  2. Swelling and Enlargement: Mammary tumors can cause swelling and enlargement of the affected gland(s). This may result in asymmetry or changes in the size and shape of the mammary glands. In some cases, the swelling may extend beyond the mammary glands into the surrounding tissues.
  3. Changes in Mammary Gland Texture: The texture of the mammary gland may change in the presence of a tumor. It may feel harder, firmer, or lumpy compared to the surrounding healthy tissue.
  4. Discharge: Mammary tumors can cause various types of discharge from the affected gland(s). This discharge may be bloody, pus-like, or clear in appearance. It is important to note any changes in the color, consistency, or odor of the discharge.
  5. Ulceration and Open Sores: Advanced or aggressive mammary tumors may lead to ulceration or the development of open sores on the surface of the skin. These sores may be painful, prone to bleeding, or become infected.
  6. Lymph Node Enlargement: As mammary tumors progress, they can spread to the regional lymph nodes. In such cases, you may notice enlarged, firm, or tender lymph nodes in the armpit or inguinal area. Lymph node involvement indicates a more advanced stage of the disease.
  7. Behavioral Changes: Dogs with mammary tumors may exhibit changes in their behavior or overall health. They may appear lethargic, have a decreased appetite, experience weight loss, or show signs of discomfort or pain.

It is important to note that while these symptoms can be suggestive of mammary tumors, they are not exclusive to this condition. Other conditions, such as mastitis or cysts, can also present with similar signs. Therefore, it is crucial to have any suspicious masses or changes evaluated by a veterinarian for a definitive diagnosis.

Natural Ways to Help Dogs with Tumors

Herbs and specific food supplements, such as TCMVET Baituxiao Mix Herbs and Mushrooms, benefit dissolving and shrinking various tumors and lumps inside and outside of dogs and cats. They also promote blood circulation and eliminate blood stasis.
It inhibits tumor growth and metastasis, and regulates cancer cell apoptosis. It softens lumps, relieves inflammation, reduces pain, and stops tumor bleeding.
It promotes postoperative healing and blood supplementation. It effectively reduces the postoperative recurrence rate, improves pets’ quality of life, and extends their lifespan.

It’s crucial to remember that these symptoms don’t necessarily mean your dog has mammary tumors, as they can also be signs of other conditions. If you notice any of these signs, it’s wise to seek veterinary advice as soon as possible to get a proper diagnosis and treatment plan. Regular veterinary check-ups can catch such conditions early, improving your dog’s prognosis.


Accurate diagnosis of mammary tumors requires a comprehensive approach. It typically involves a thorough physical examination, fine-needle aspiration or core needle biopsy, and histopathological analysis. Imaging techniques such as radiographs, ultrasound, or advanced imaging modalities like computed tomography (CT) or magnetic resonance imaging (MRI) may be employed to assess tumor size, local invasion, and the presence of metastasis.

Treatment Options

The primary treatment for mammary tumors in both dogs and cats is surgical excision, which involves removal of the tumor mass along with the surrounding mammary tissue. In dogs, regional lymph node removal is often performed concurrently. The extent of surgery depends on factors such as tumor size, location, number of affected glands, and the presence of metastasis. Adjuvant therapies such as radiation therapy, chemotherapy, or targeted therapies may be recommended based on the tumor’s characteristics and stage.


The prognosis for mammary tumors in dogs and cats varies depending on several factors, including tumor type, size, grade, lymph node involvement, presence of metastasis, and the completeness of surgical removal. Generally, the prognosis is better for benign tumors and those with early detection and complete surgical excision. Malignant tumors, especially those with regional lymph node or distant organ involvement, have a less favorable prognosis. Regular follow-up examinations, including physical examinations and imaging, are essential to monitor for tumor recurrence or metastasis.


Mammary tumors are a significant concern in intact female dogs and cats, with a higher prevalence in dogs. Early detection, accurate diagnosis, and appropriate treatment are crucial for achieving better outcomes. Spaying female cats before their first heat cycle can significantly reduce the risk of developing mammary tumors. Owners should consult with their veterinarian to develop a proactive approach to mammary tumor prevention, early detection, and treatment to optimize the health and well-being of their pets.

Brenda Thompson

Brenda Thompson is an expert in dog behavior with over a decade of experience, and she is also passionate about working with cats and birds. In addition to contributing pet content to, she is a Certified Dog Behavior Consultant. She received her Doctorate of Veterinary Medicine (DVM) from Ross University School of Veterinary Medicine in 2007 and has over 16 years of experience in treating animals. Her expertise is in educating pet owners on common pet health problems and providing them with option-based care to help choose what is best for their companions

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