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Mammary Gland Tumors in Dogs

What Are Mammary Gland Tumors in Dogs?

Mammary gland tumors in dogs are abnormal growths that develop in the mammary glands, which are located on the abdomen of female dogs. These glands, numbering five pairs, serve the purpose of providing milk and nutrients to puppies. Typically found beneath the armpits and extending toward the groin area, they become more prominent in female dogs that have had litters.

Typically, female dogs are spayed at a young age, but those that aren’t may go on to have litters during their lifetime. Dogs with prior litters often have more noticeable mammary glands, which can be observed visually or by touch.

Approximately half of mammary tumors in dogs are cancerous (malignant). These tumors can be of various types:

  • Benign adenomas (non-cancerous)
  • Mammary carcinomas (cancerous)
  • Mammary sarcomas (cancerous)
  • Mixed mammary tumors (which can be either non-cancerous or cancerous)
  • Inflammatory carcinoma (highly malignant and aggressive)

Regular veterinary check-ups should include examination of the dog’s mammary glands to detect any abnormalities early on. This helps in timely diagnosis and management of mammary gland tumors in dogs.


Symptoms of mammary gland tumors in dogs may include changes in the texture of the glands, which should normally be soft and pliable. Any presence of lumps or firm swellings warrants immediate examination by a veterinarian.

Additionally, dogs with mammary tumors might display other symptoms such as:

  • Tenderness, warmth, or pain around the tumor site
  • Lethargy
  • Reduced appetite and weight loss
  • Weakness
  • Coughing

Being attentive to these signs and promptly seeking veterinary care can aid in the early detection and management of mammary gland tumors in dogs.


Mammary gland tumors are frequently observed, particularly in female dogs that have not been spayed, as hormones such as estrogen and progesterone influence both mammary development and the formation of cancer. However, the exact cause remains unknown.

In dogs that have been spayed, mammary tumors are less common. The risk of developing a mammary tumor in a dog spayed before her first heat cycle is approximately 0%. However, if the dog is spayed after her first heat cycle, the likelihood of mammary tumor development increases to about 8%. For dogs that undergo two or more heat cycles, the risk of developing a mammary tumor rises to approximately 25%.

While only around half of these tumors are cancerous, it is crucial to take any tumor seriously and conduct further testing for accurate diagnosis. Early detection and appropriate management are vital in addressing mammary gland tumors in dogs.


Veterinarians employ several methods to diagnose mammary gland tumors in dogs. During a physical examination, the veterinarian will palpate (touch) the mammary mass to assess its characteristics. Benign tumors often feel like small, well-defined, firm masses, while malignant tumors are typically adhered to underlying tissues, immobile, and have unclear borders.

Basic blood work may be conducted alongside a fine needle aspirate, where a needle is inserted into the mass to collect cells for laboratory analysis. While this test is usually performed on an outpatient basis, it does have some limitations. Additionally, the veterinarian may opt for a biopsy, involving the removal of skin or mass tissue for further diagnosis.

If results indicate cancer, follow-up examinations such as chest radiographs and abdominal ultrasounds may be recommended, as mammary tumors commonly metastasize to local lymph nodes, the chest, and potentially the liver.

Tumors that are large, have metastasized to other organs, are ulcerated, exhibit rapid growth, or are attached to deeper tissues like the muscle layer, unfortunately, carry a poor prognosis. Survival times for such cases range from several months to several years. Early detection and comprehensive evaluation are crucial for effective management of mammary gland tumors in dogs.


Surgery is typically recommended for effectively managing polyps. Removal of the polyps can be done

The primary treatment for mammary gland tumors in dogs typically involves surgical intervention. Chemotherapy and radiation may be considered if the tumor is particularly large, has been incompletely excised during surgery, or has already spread to other areas, but surgical removal remains the preferred treatment option.

Non-cancerous tumors can often be left untreated unless they pose cosmetic concerns or discomfort to the dog. However, regular monitoring for any changes in size or consistency is recommended.

There are five main types of surgeries for mammary gland tumors in dogs:

  • Lumpectomy: Removal of the mass only.
  • Simple mastectomy: Removal of the mass and the associated gland.
  • Regional mastectomy: Removal of the mass, associated gland, and nearby glands and lymph nodes.
  • Radical or unilateral mastectomy: Complete removal of the entire mammary chain on one side.
  • Bilateral mastectomy: Removal of both mammary chains.

Each surgical approach is tailored to the specific characteristics of the tumor and the dog’s overall health. Early detection and appropriate surgical intervention play crucial roles in the successful treatment of mammary gland tumors in dogs. Regular follow-up examinations are important to monitor the dog’s condition post-surgery and ensure optimal recovery.

the anal opening, followed by closure of the opening with stitches. Alternatively, endoscopic removal or the use of an electrical needle or probe may be employed for the same purpose. Medications that may be prescribed include non-steroidal pain relievers, antibiotics (especially before surgery to prevent infection), and stool softeners. Potential complications may include polyp recurrence and narrowing of the anal opening due to scarring and/or inflammation.

Living and Management

Preventative care for mammary gland tumors in dogs primarily involves ensuring timely spaying, especially at a young age. If you adopt a dog with a history of litters or an unknown reproductive background, consulting your veterinarian is essential to discuss spaying options and mitigate potential mammary gland complications.

Following the diagnosis and surgical removal of mammary gland tumors, your veterinarian will likely advise scheduled follow-up appointments to monitor your dog’s recovery and overall health. Regular veterinary care is crucial for ensuring the well-being of your dog post-surgery and managing any potential complications effectively.

Mammary Gland Tumors in Dogs FAQs

What is the life expectancy of dogs with malignant mammary gland tumors?

The average survival time for dogs diagnosed with malignant mammary tumors varies depending on factors such as the tumor type (sarcoma vs. carcinoma), stage, extent of tumor spread, invasiveness, and grade. Survival times can range from as short as 1 month to nearly 2 years, contingent upon the specific diagnosis of the dog.

How do you get rid of mammary gland tumors in dogs?

The primary treatment for these tumors involves surgical removal. Although chemotherapy and radiation are additional therapy options, surgical removal is usually necessary for mammary tumors.

What does a mammary tumor look like on a dog?

Mammary tumors in dogs typically present as spherical masses of different sizes protruding from the abdomen’s skin. These tumors often feel like small, firm masses located on, near, or around the gland. Some may seem anchored to deeper structures beneath the skin, making them immobile, with indistinct borders.

Are mammary tumors in dogs painful?

Mammary tumors in dogs can frequently cause pain and discomfort, emphasizing the importance of having your dog examined. Your veterinarian may recommend diagnosing and treating the condition, possibly prescribing pain medication to alleviate discomfort.

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