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Signs of Breast Cancer in Dogs

Signs of Breast Cancer in Dogs

Mammary cancer is the most commonly diagnosed tumor in intact female dogs that are older than seven years of age. Our Long Island vets share some signs and treatments for this condition.

What is Breast Cancer In Dogs?

Breast cancers in dogs are often referred to simply as mammary tumors. A mammary tumor develops as a result of abnormal replication of the cells that make up the breast tissue. Mammary tumors can be benign (non-cancerous) or malignant (cancerous). 

This disease usually strikes approximately one in four unspayed female dogs. Females spayed before their first estrus cycle reduce the chances from 25% to .05%. If spayed after their first heat, but before the second, the risk of future breast cancer is approximately 8%. Half of the mammary tumors found in canines are benign, and of the half that are malignant, most can be successfully treated with surgery if caught early enough.

Breast cancer in canines is relatively common, occurring in approximately 25% of unspayed female dogs. Although it is rare, male dogs may also develop breast cancers. Breast cancer in males tends to metastasize aggressively.

What causes this cancer?

The exact causes for the development of mammary tumors in dogs are not fully understood. It is well known that exposure to specific hormones, namely progesterone, increases the risk of developing mammary cancers in dogs. This is because progesterone stimulates growth factors (molecules that stimulate specific processes in the body) that cause mammary cells to multiply.

Hereditary factors, although important in humans, have not been definitively linked to mammary cancer in dogs. Low-risk breeds include the boxers and chihuahuas. High-risk breeds include poodles, English spaniels, English setters, and terriers. Early spaying has been shown to dramatically reduce the risk for mammary cancer.

Symptoms of Breast Cancer in Dogs

Most of the signs of breast cancer are related to the tumors themselves and are located on one of the eight to ten mammary glands present on most female canines. The majority of tumors are found near the mammary glands closest to the back legs. Signs can include:

  • Bloody discharge or pus from nipple
  • Multiple bumps
  • Painful or swollen breasts
  • Singular lumps
  • Ulceration 
  • Yellow discharge or pus from nipple

Systemic symptoms that might indicate cancer could include:

  • Breathing difficulties
  • Coughing
  • Lameness
  • Lethargy
  • Loss of appetite
  • Weakness
  • Weight loss
  • Enlarged lymph nodes

How To Diagnose Breast Cancer in Dogs

Your veterinarian will start your appointment by palpating the mass or masses and collecting data regarding their size, hardness, and mobility. Information about your dog’s health history, including applicable information about your animal’s last heat cycle, current medications, and information about pregnancies will be collected. X-rays and ultrasound may be used to visualize the spread, but they may not identify any microscopic dissemination of the cancer cells. 

A veterinary oncologist will usually recommend a biopsy of any tumors, and for the lymph nodes. General testing is done to check for any concurrent disorders, and a complete blood count, urinalysis, and blood chemistry profile will be used to evaluate the condition of the patient. This is done to ensure that the animal is healthy enough to undergo surgery and the anesthesia required. A biopsy of the tumor, after surgical removal, is usually necessary for a definitive diagnosis.

Treating Breast Cancer in Dogs

For dogs with solitary mammary tumors, surgery is by far the best treatment. If there is only one small mass and staging shows no evidence of spread, surgery may be the only treatment your dog receives.

For dogs with multiple tumors of one or both mammary chains, the associated – or all – of the mammary glands may need to be removed. If your dog is intact, an ovariohysterectomy (spay) is recommended and may be done at the same time as the mammary gland removal.

For dogs with larger tumors or evidence of spread to other areas of the body, chemotherapy is typically recommended. There is increasing evidence that radiation therapy may provide some benefit for dogs with inflammatory carcinomas in addition to chemotherapy. Your veterinarian will discuss the options that are best suited for your dog’s particular situation.

Note: The advice provided in this post is intended for informational purposes and does not constitute medical advice regarding pets. Please note that Atlantic Coast New York Veterinary Specialists does not offer oncology services.

If you've noticed a new lump or bump on your dog, contact our vets for a diagnosis and treatment options. 

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